Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a mental health condition that can develop after a person experiences, witnesses, or learns of a traumatic event. What separates it from the ordinary distress that follows a frightening experience is persistence: symptoms continue well past the period in which most people recover. These symptoms typically include intrusive re-experiencing, avoidance, negative changes in mood and cognition, and heightened arousal. PTSD is classified among trauma- and stressor-related disorders and often overlaps with anxiety disorders and depression.

Published prevalence figures put the global rate near four percent of people, while lifetime estimates for the United States fall around six to eight percent. Rates run higher among women and veterans. Because the condition can be chronic and is linked with other psychiatric illness, substance use, physical disease, and mortality, it is a significant concern for public health as well as for individual patients.

This entry covers the core symptoms and the diagnostic criteria used in DSM-5-TR and ICD-11, including the separate ICD-11 diagnosis of complex PTSD. It then reviews epidemiology, risk and protective factors, course and comorbidity, and the neurobiological findings that underpin current models. The entry also addresses assessment, psychological and pharmacological treatments, and special populations, ending with the historical development of the concept and its unresolved debates.

Definition and Core Symptoms

Post-traumatic stress disorder (PTSD) is a trauma- and stressor-related disorder. It develops after exposure to a traumatic event and is defined by a cluster of characteristic symptoms that persist well beyond the immediate aftermath. Diagnosis follows a sequence: an identifiable exposure, symptoms from several domains, and a duration and level of disruption that separate the condition from an expected reaction to danger.

Trauma exposure as the precondition

In DSM-5-TR, the exposure criterion requires actual or threatened death, serious injury, or sexual violence. It can be met in four ways. The first is direct experience of the event. The second is witnessing it in person as it happens to others; events seen only on television, in films, or in other electronic media do not count. The third is learning that the event happened to a close family member or friend. If the event was a death, or a threatened death, it must have been violent or accidental. The fourth is repeated or extreme exposure to aversive details of other people's trauma, which typically applies to professionals such as first responders who collect human remains or police officers who repeatedly review records of child abuse. Media exposure generally does not qualify unless it is work-related.

Each route is recognised differently in practice. Direct experience and in-person witnessing are usually documented by recording what happened, where, and how close the person was. Indirect routes require the clinician to establish the relationship to the affected person and, for deaths, the manner of death. Occupational exposure requires an account of how often and how severely the person was exposed to the distressing details. Ordinary life stressors, such as divorce or financial crisis, do not meet the criterion on their own.

The four symptom domains

Clinical description organises PTSD symptoms into four clusters: intrusion, avoidance, negative alterations in cognition and mood, and marked alterations in arousal and reactivity.

Intrusion refers to re-experiencing the event. It includes recurrent, involuntary, and distressing memories; traumatic nightmares; and dissociative reactions such as flashbacks, which can range from brief episodes to a near-complete loss of awareness of the present. It also includes intense distress and marked physiological responses when the person meets reminders of the event.

Avoidance refers to effortful attempts to stay away from trauma-related thoughts, feelings, and external cues such as particular people, places, conversations, or activities.

Negative alterations in cognition and mood cover persistent, distorted blame of oneself or others; exaggerated negative beliefs about oneself or the world; a lasting negative emotional state such as fear, shame, guilt, or anger; reduced interest in previously enjoyed activities; a sense of detachment from others; and a persistent inability to experience positive emotions. Difficulty recalling key features of the event, often attributed to dissociative amnesia, also belongs here. This cluster is the one most closely associated with emotional numbing.

Alterations in arousal and reactivity include sleep disturbance, irritability or angry outbursts, reckless or self-destructive behaviour, difficulty concentrating, hypervigilance (a constant sense of being on guard), and an exaggerated startle response. DSM-5 explicitly acknowledges that this cluster can present as aggression as well as the withdrawn, "flight" pattern of earlier formulations.

Concrete manifestations

The clusters become recognisable in daily life. A person may hear a car backfire and feel briefly back in a combat zone, wake repeatedly from nightmares about a robbery, or reroute every journey to avoid a street where an assault occurred. Someone may describe feeling emotionally flat, unable to feel affection for family, and convinced the world is unsafe. Others may sit facing the door in every room, startle at small noises, or sleep poorly despite exhaustion. These experiences are not diagnostic on their own; what matters is that they cluster together, persist, and interfere with functioning.

Distinguishing PTSD from normal fear, grief, and acute reactions

Fear after a dangerous event is adaptive, and intrusive memories, jumpiness, and poor sleep are common in the days that follow. Most of these reactions fade. PTSD is distinguished by persistence and by functional impairment. Its symptoms must cause clinically significant distress or impair social, occupational, or other important areas of life, and they must not be explained by a substance or a medical condition.

Grief is a separate problem. It centres on loss and longing, whereas PTSD centres on threat and re-experiencing, although the two can coexist, particularly after a violent or accidental death of a loved one, which is one of the exposure routes described above.

The clearest boundary is with acute stress disorder (see acute stress disorder). DSM-5-TR assigns symptoms lasting from three days to one month after the event to acute stress disorder, and requires symptoms to persist for more than one month before PTSD is diagnosed. The distinction is therefore largely one of time, but the clock does not settle every case. Some people first show symptoms months or even years after the trauma, a pattern known as delayed expression, so a late onset does not rule out PTSD. Clinicians therefore weigh the timing of symptoms together with their severity and the degree of impairment, rather than relying on the one-month threshold alone. Overlap with anxiety disorders and depression is common, which is why the symptom history must be checked against the trauma timeline.

Diagnostic Criteria in DSM-5-TR and ICD-11

The two principal classification systems, the American Psychiatric Association's DSM-5-TR and the World Health Organization's ICD-11, both describe PTSD as a disorder that follows exposure to trauma, but they differ in how they define the triggering event, how many symptoms they require, and how they handle time and impairment. These differences are not cosmetic: they change who receives the diagnosis.

Exposure requirement

DSM-5-TR limits the qualifying event to actual or threatened death, serious injury, or sexual violence. The event counts when it is experienced directly, witnessed in person, or learned about as having happened to a close family member or friend; in the last case, a death must have been violent or accidental. DSM-5-TR also counts repeated or extreme exposure to aversive details, which is why first responders and police officers handling child-abuse cases can qualify. ICD-11 instead requires exposure to an extremely threatening or horrific event. This wording does not list specific harms, so it is broader in scope and leaves more to clinical judgement about what counts as traumatic.

Symptom structure and thresholds

DSM-5-TR uses four symptom clusters, labelled B to E. It expanded the three-cluster structure of DSM-IV after factor-analytic studies favoured a four-factor model. Its thresholds are: at least one of five intrusion symptoms (B); at least one of two avoidance symptoms (C); at least two of seven symptoms that combine negative cognitions and mood with dissociative features (D); and at least two of six arousal and reactivity symptoms (E). The total symptom pool is twenty items.

ICD-11 reduces the model to three core clusters: re-experiencing the trauma in the present, avoidance of reminders, and a persistent sense of current threat. All three must be present, and there is no numerical threshold within each cluster beyond that. ICD-11 also drops sleep and concentration difficulties, which overlap with many other disorders, in order to improve the specificity of the diagnosis. Its framing treats PTSD primarily as a conditioned fear response, with re-experiencing and avoidance tied closely to the specific traumatic event.

Duration and functional impairment

DSM-5-TR requires that the disturbance last more than one month and cause clinically significant distress or impairment in social, occupational, or other important areas of functioning. ICD-11 also requires functional impairment, with symptoms persisting for at least several weeks. The impairment requirement was introduced into ICD-11 partly to separate PTSD from normal reactions to extreme stress, because the ICD-10 threshold was seen as relatively low.

Rationale for the ICD-11 approach

The ICD-11 developers aimed to make the diagnosis more clinically useful. Factor-analytic research suggested that PTSD could be captured reliably by a smaller set of symptoms that cohere statistically and clinically. Narrowing the criteria was also intended to reduce comorbidity artefacts, in which a broad diagnosis absorbs symptoms that belong to other conditions.

Effects on diagnostic rates

The practical effect on prevalence is inconsistent across studies. Most studies, mainly in adults, found that ICD-11 yields lower rates than DSM-5. A Japanese web survey of 6,180 people found that ICD-11 gave lower PTSD caseness than DSM-IV, DSM-5, and ICD-10, while DSM-5 and ICD-11 showed substantial agreement. Among internally displaced people in Ukraine, DSM-5 gave 27.4% and ICD-11 gave 21.0%, with ICD-11 cases showing higher disability. By contrast, a 2020 study of Chinese earthquake survivors nine and a half years after the event found higher prevalence under ICD-11, while a study of Chinese adolescents found no significant difference, and a military sample showed 48% under ICD-11 against 56% under DSM-5, a gap that was not statistically significant. Some earlier comparisons also relied on DSM-based instruments to estimate ICD-11 symptoms, which limits their comparability. Measures built for each system, such as the PCL-5 and the International Trauma Questionnaire, have since been used for more direct comparison.

Complex PTSD and Differential Diagnosis

Complex PTSD in ICD-11

ICD-11 treats complex PTSD as a parallel diagnosis that builds on the standard PTSD picture rather than replacing it. The proposed ICD-11 complex PTSD requires PTSD symptoms but also adds three features that reflect how trauma can disturb the systems of self-organisation governing affect, self-concept, and relationships. These added features, termed disturbances of self-organisation (DSO), are defined by three clusters: affect dysregulation, negative self-concept, and disturbances in relationships. In practice, this means severe emotional reactivity or numbing, a lasting sense of being worthless or defeated, and persistent trouble sustaining close bonds. Unlike the fear or horror of core PTSD, which is tied to trauma-related stimuli, these disturbances are pervasive and appear across contexts and relationships regardless of proximity to reminders. Diagnosis requires the presence of PTSD as well as at least one symptom in each of the three self-organisation features, and the disturbance must produce significant impairment across personal, social, educational, or occupational functioning.

Absence from DSM-5-TR and the Validity Debate

The American Psychiatric Association's system has not adopted complex PTSD as a separate entity. The specific CPTSD diagnosis is not currently separated from PTSD in the DSM but has been recognised by the ICD-11. DSM-5-TR offers only two specifiers for PTSD, one for dissociative symptoms and one for delayed expression, the full diagnostic criteria are not met until at least 6 months after the event. Before DSM-5, the condition was listed as disorders of extreme stress, not otherwise specified (DESNOS) in DSM-IV, and it was later placed under the unspecified trauma- and stressor-related category.

The main reason given for exclusion is an overlap finding. During the DSM-IV trials, Roth and colleagues found that 92% of individuals who had the proposed complex PTSD diagnosis also met the criteria for PTSD. This was the reason it was not included in DSM-5. A 2012 review by Resick concluded there was not enough empirical support for a distinct disorder, citing a lack of definitional consensus, a lack of reliable and valid measures, and uncertainty over whether it is a separate disorder or a more severe form of PTSD. Critics of exclusion argue that many people with prolonged trauma present with symptoms of depression, anxiety, or dissociation, or of borderline personality disorder rather than classic PTSD. Some empirical work supports the construct: a latent profile analysis of trauma survivors identified a class with elevated symptoms of CPTSD (PTSD symptoms and disturbances in self-organization), and cross-national factor analyses have generally supported a two-cluster structure.

Differential Diagnosis

Acute stress disorder shares intrusion, avoidance, dissociation, and arousal symptoms with PTSD, but DSM-5-TR restricts it to the period from roughly three days to one month after exposure. Symptoms that persist beyond that window and meet full criteria shift the diagnosis toward PTSD. Adjustment disorder, by contrast, does not require a Criterion A event; it is diagnosed when distress or impairment follows an identifiable stressor within three months and full criteria for another disorder are not met.

Major depression is among the most frequent confounders. Sleep disturbance, detachment, anhedonia, and negative cognitions appear in both conditions, and clinicians need to look for the features that are more specific to trauma: intrusive re-experiencing, trauma-linked fear, avoidance of reminders, and hypervigilance. Bipolar disorder overlaps through irritability, impulsivity, and sleep disruption. A lifetime history of mania or hypomania should be explored before treatment, because antidepressants commonly used for PTSD can precipitate mood switching.

Borderline personality disorder (BPD) is the most consequential differential for complex presentations. Studies have found that approximately half of individuals diagnosed with cPTSD also meet criteria for BPD, which may reflect shared features that complicate the diagnostic process rather than simple comorbidity. Evidence suggests the two are separable: BPD can be distinguished by fear of abandonment, impairment in interpersonal relationships, impulsivity and an unstable sense of self. The overlap does not mean one is a subtype of the other; researchers have argued that BPD and cPTSD overlap substantially, but it is unwarranted to conceptualize cPTSD either as a replacement for BPD, or simply as a sub-type of BPD.

Dissociation cuts across all these categories. Dissociation is a core symptom of various disorders, including dissociative disorders, (complex) post-traumatic stress disorder, and borderline personality disorder. Up to 80% of patients with BPD report transient dissociative symptoms, such as derealisation, depersonalisation, and numbing. DSM-5-TR accordingly provides a specifier for PTSD with dissociative symptoms, while dissociative identity disorder and depersonalisation/derealisation disorder remain separate diagnoses with their own criteria.

Implications for Assessment

Symptom overlap can both mask and mimic PTSD. A depressive or dissociative presentation may conceal re-experiencing and avoidance, while emotional dysregulation and unstable relationships can lead clinicians to a BPD label without a trauma history being explored. In one reported case, a patient's diagnosis was changed from BPD to cPTSD after she was admitted in an acute inpatient mental health unit, illustrating how the initial impression can shift with fuller history-taking.

Instrument choice also matters. The PCL-5 was developed prior to the emergence of ICD-11 criteria for CPTSD and therefore was not designed to explicitly capture CPTSD-specific symptoms. By contrast, the International Trauma Questionnaire does include 6 DSO-specific items, addressing the three subfacets with two items each. Assessment should therefore map symptoms against each diagnostic framework, document the timing of symptoms relative to the event, screen for lifetime mania, and record dissociative episodes, since these details often determine which diagnosis fits.

Epidemiology and Prevalence

Global and national estimates

The largest cross-national evidence comes from the World Health Organization's World Mental Health Surveys. Drawing on 26 population surveys and 71,083 respondents ages 18+, the project used the Composite International Diagnostic Interview to assess both trauma exposure and PTSD. Its lifetime estimate stood at 3.9 percent across whole populations and rose to 5.6 percent among people with a trauma history (The cross-national lifetime prevalence of PTSD was 3.9% in the total sample and 5.6% among the trauma exposed.). Exposure itself is far more common than the disorder: 70.4% of respondents experienced lifetime traumas, with exposure averaging 3.2 traumas per capita. The conditional figure of 5.6 percent therefore means that only about one exposed person in eighteen goes on to develop PTSD.

National figures vary with the instrument and time frame used. In the United States, past-year and lifetime prevalence estimates were 4.7% and 6.1%, respectively. Clinical reviews give a wider range, reporting that the lifetime prevalence of posttraumatic stress disorder (PTSD) ranges from 6.1 to 9.2 percent in national samples of the general adult population in the United States and Canada. Income level also matters in the WMH data: High income countries (5.0%) had twice the proportion of PTSD cases as upper-middle income (2.3%) and lower-low middle income countries (2.1%). Among trauma-exposed people the gap persisted, with rates of 6.9% in high-income countries against 3.9% in upper-middle income countries. Lower reported rates in poorer countries may partly reflect differences in exposure measurement, access to diagnosis, and survey design rather than a true lower burden, and the data do not settle this.

Sex differences

Women consistently show higher lifetime rates. The lifetime prevalence of PTSD is about 10–12% in women and 5–6% in men. Reviews describe the female excess as roughly two- to threefold. Part of this gap reflects exposure. Women in a Dutch nationally representative sample were far more likely to report sexual violence (22.8 % vs 4.4 % in men), whereas men more often reported non-interpersonal trauma. Yet the excess does not disappear once trauma type is taken into account: the increased prevalence of PTSD in women remains even when trauma type is controlled for. Women's episodes also tend to last longer, a point taken up in the course section.

Variation by trauma type

Interpersonal violence carries the greatest risk. In the WMH analysis, traumas involving interpersonal violence had highest risk. A U.S. national study found a similar ordering, with the highest conditional rates among victims of interpersonal violence and combat. In its event-level table, the composite lifetime PTSD estimate was 10.1 percent after disasters and 15.3 percent after sexual or physical assault (Disaster | 1,491 | 10.1 | 1.0 | 0.4 | 0.1 | ... Sexual/physical assault | 1,568 | 15.3 | 1.2 | 7.3 | 0.9). Sexual assault stands out in particular. One meta-analysis reports that 36% of sexual assault survivors meet criteria for lifetime PTSD, and the course differs by trauma type: among violent traumas the median prevalence rose from 11.8 percent at one month to 23.3 percent at twelve months, while for non-violent traumas it fell over the same period (PTSD prevalence decreased over time for non-violent traumas (20.1% at month 1 and 14.0% at month 12)).

Higher-prevalence subgroups

Some groups have elevated rates. PTSD prevalence has been consistently found to be higher among certain subgroups, including women and military veterans. Among adult survivors of war in conflict-affected countries, a 2019-era meta-analysis reported a point prevalence of 26.51% for PTSD, which is a different measure from lifetime prevalence and should not be compared directly with the general-population figures above.

Methodological sources of variation

Estimates depend heavily on how cases are identified. One umbrella review notes that PTSD point prevalence varies widely, even when regarding a traumatic event of the same nature. Structured interviews such as the CIDI apply diagnostic rules in full, whereas self-report symptom questionnaires generally capture a broader set of distress and tend to produce different figures. Inclusion rules also shape pooled results: a meta-analysis of preschool children required that PTSD was assessed using standardized interviews at least 1-month post trauma. Differences in time frame (30-day, 12-month, or lifetime), in sampling frames, and in the wording of exposure questions further complicate cross-study comparison, and the sex and income differences described above should be read with these limits in mind. Epidemiological comparisons of this kind are also confounded by differences in trauma exposure, which is why exposure-adjusted rates are preferred in statistical analyses.

Risk and Protective Factors

Most people who face a potentially traumatic event never develop PTSD. Global estimates suggest that roughly 70% of people will encounter such an event at some point, yet only about 5.6% go on to develop the disorder, and the risk varies with the kind of event involved (https://www.who.int/news-room/fact-sheets/detail/post-traumatic-stress-disorder). <!-- placeholder removed below -->

Pre-trauma factors

Several characteristics that exist before the event raise vulnerability. Reviews commonly list prior trauma, both in adulthood and in childhood, a family history of psychopathology, and personality traits such as neuroticism (psychscenehub review). Childhood adversity is a particularly consistent finding: it is associated with a higher chance of PTSD after an adult trauma, with more severe symptoms, and with a lower likelihood of recovery once the disorder has developed (medRxiv study). Genetic and gene-environment interactions are also proposed; for example, one serotonin transporter variant combined with childhood adversity has been linked to greater risk (psychscenehub review). These mechanisms are discussed in the genetics and epigenetics sections.

Sex and prior psychiatric history also matter. In one US survey using DSM-III-R criteria, lifetime PTSD was reported in about 10.4% of women and 5% of men (Cambridge review). Across studies, PTSD has been more prevalent among women, unmarried people, those with less education, and people with a psychiatric history (PTSD and peritraumatic dissociation review). In children, Danish registry data link neurodevelopmental disorders such as autism spectrum disorder and ADHD to a higher risk of PTSD (Springer cohort study).

Peritraumatic factors

Features of the event itself and of the person's state during it are among the strongest predictors. Event severity, perceived threat to life, emotional distress, and dissociation during the trauma are all listed as risk factors (psychscenehub review). In children and adolescents, a meta-analysis of 32 studies found that perceived threat and fear during the event had a medium-sized association with later PTSD, whereas dissociation had a weaker one (PubMed meta-analysis; ScienceDirect meta-analysis).

Peritraumatic dissociation is the most debated factor. A 2007 meta-analysis of 35 studies found a moderate average correlation with PTSD, and the authors judged it a moderate risk factor (PubMed meta-analysis). Other reviews have described it as the strongest predictor among pre- and post-trauma variables (PMC review). However, many of those studies were retrospective, and symptom severity may have shaped how people remembered dissociating; prospective data are therefore considered more convincing (PMC rodent-model article). Because the study designs did not allow causal conclusions, the link is still regarded as associative (ResearchGate meta-analysis).

The interpersonal nature of an event also increases risk. Interpersonal trauma is among the strongest indicators in children, alongside low social support and intense fear (Psychiatrist.com summary). When a family member is the perpetrator, the child is also left without a safe source of support (Springer cohort study). Physical injury, entrapment, and bereavement are included among severe exposures associated with higher PTSD rates (PTSD and peritraumatic dissociation review).

Post-trauma factors

Support after the event appears to matter. The WHO notes that feeling supported by family, friends, or others after a trauma can reduce the risk of PTSD (WHO fact sheet). A meta-analysis of adolescents found that low social support predicted PTSD (ScienceDirect study), but a later adolescent study found that support lost its significance once childhood adversity and other covariates were controlled, so its independent contribution remains uncertain (ScienceDirect study). Ongoing stressors and the absence of support in the weeks after a trauma are also listed as risk factors (psychscenehub review). Anxiety symptoms and dysfunctional coping in the early aftermath have been associated with later PTSD (PTSD and peritraumatic dissociation review). The effects of early medical treatment after trauma are less settled in the evidence base and are covered in the treatment and prevention sections.

Resilience

Resilience is the reason PTSD is the exception rather than the rule. A 2023 review notes that most people exposed to trauma do not develop PTSD or other forms of psychopathology (Nature Reviews Psychology review). In a meta-analysis of longitudinal trajectories, a resilient pattern with low symptoms was the most common, observed in about two-thirds of participants on average (Nature Reviews Psychology review). The same review argues that binary diagnosis tells us little about how resilient adaptation actually develops, and it points to regulatory flexibility as a candidate mechanism (Nature Reviews Psychology review). Some people even report gains such as greater self-confidence or stronger relationships after adversity (ClinicalTrials.gov description).

Resilience is also linked to lower PTSD symptoms in situations of large-scale stress. During the COVID-19 pandemic, people with higher psychological resilience adapted better and showed lower PTSD levels despite significant adversity (MECP meta-analysis). Taken together, the evidence suggests that PTSD arises from the interaction of how severe an event is, how the person experienced it, and what supports and vulnerabilities existed before and after it, rather than from exposure alone, which is why most exposed people recover without developing the disorder.

Course, Recovery and Comorbidity

Trajectories over time

PTSD does not follow a single course. A 2018 review of 54 studies by Galatzer-Levy and colleagues described four recurring symptom trajectories: resilience, recovery, chronicity, and delayed onset, with delayed onset the least frequent. In a systematic review of directly exposed populations, about one third of people with PTSD remitted within three months, while 39% had a chronic course. Onset after three months accounted for only about 3.5% of cases. Estimates of how many patients have recovered by the two-year mark vary widely between cohorts, which differ in trauma type, treatment received, and length of follow-up.

Over longer periods the pattern is similar but more fluid. In a 12-year follow-up that began roughly three decades after a war, the direct-exposure group contained about 43% resilient, 28% recovered, 21% chronic, and 8% delayed-trajectory cases. A 20-year study of Israeli veterans of the Lebanon War documented fluctuating remissions and relapses rather than a steady decline. Clinically, the chronic and delayed groups are the ones that most often need targeted intervention, because they are least likely to resolve without it.

Comorbidity and its effect on outcome

PTSD frequently occurs alongside other disorders, most often unipolar depression, anxiety disorders, and substance use disorders. Among people in treatment for substance use disorders, roughly 20–50% have a lifetime diagnosis of PTSD, and about 20% of treatment-seeking PTSD patients meet criteria for a current substance use disorder. Comorbid presentations are associated with more severe PTSD, more severe substance use, and poorer treatment outcomes for both conditions. One proposed explanation is self-medication of trauma symptoms, although the direction of effect remains unclear in prospective data. Clinically, episodes of re-experiencing have been linked to craving and relapse, while abstinence has been associated with a rise in PTSD symptoms.

Depression is a central part of this picture. In a randomized trial of 81 veterans with PTSD and substance use disorders, an integrated exposure-based treatment reduced depressive symptoms more than relapse prevention did, and the reduction in depression was mediated by lower PTSD severity rather than by reduced substance use. This suggests that depressive symptoms in comorbid cases may partly track PTSD itself. The evidence on links with bipolar disorder and borderline personality disorder is thinner, and differentiating these presentations is discussed in the differential diagnosis section.

Physical health consequences

PTSD is associated with excess physical morbidity and mortality. A 2013 meta-analysis of 402,274 participants found a 55% higher risk of incident coronary heart disease or cardiac mortality among people with PTSD. A later meta-analysis of 13 studies, covering more than 335,000 participants followed for an average of 8.6 years, reported a 49% higher risk of myocardial infarction, related hospitalization, or cardiac death after adjustment for traditional risk factors. In a cohort of over 8,000 veterans, those with PTSD were 47% more likely to develop heart failure. Proposed mechanisms include autonomic dysregulation, activation of the hypothalamic-pituitary-adrenal axis, systemic inflammation, and endothelial dysfunction, alongside maladaptive health behaviors such as smoking.

Mortality findings point the same way. A systematic review and meta-analysis of cohort studies estimated a 47% greater risk of death among people with PTSD, based on six studies providing risk or odds ratios. In the Nurses' Health Study II, which followed 51,602 women for up to nine years, the combination of PTSD and depression was associated with higher death rates from cardiovascular disease, diabetes, injury, and suicide. Sleep disturbance and chronic pain frequently accompany PTSD, but separating their contribution from that of the comorbid conditions remains difficult.

Suicide risk and prognosis

PTSD is associated with increased suicide risk, and this risk rises when PTSD co-occurs with other disorders. Among veterans, suicide attempt rates were reported to be about three times higher in those with both alcohol use disorder and PTSD. People with comorbid PTSD and substance use disorders show greater symptom severity, greater functional impairment, and higher suicidality than those with either condition alone. Comorbidity also adds to social disadvantage, with higher rates of homelessness and disability reported among patients with both conditions.

For prognosis, comorbidity is one of the strongest predictors of poor response. Treatment attrition, relapse, and persistent symptoms are more common when substance use or depression is present, which is why assessment protocols typically screen for these conditions and for suicidal ideation. Because most of these associations come from cross-sectional or observational data, the direction of causation and the shared vulnerabilities behind them are still open questions.

Neurobiological Mechanisms

Fear conditioning and extinction as a working model

Much of the neurobiological work on PTSD uses fear conditioning, in which a neutral cue acquires threat meaning through pairing with an aversive event, and extinction, in which the cue is later relearned as safe. Reviewers often describe PTSD as a disorder of fear regulation, where threat responses persist after the danger has passed. People with PTSD tend to extinguish conditioned fear poorly, and this weakness is linked to reduced control of amygdala activity by the ventromedial prefrontal cortex (vmPFC). Extinction is also fragile in healthy people. Its success depends on timing relative to the original conditioning and on stress. Animal work helps explain why. In rodents, noradrenergic input from the locus coeruleus to the amygdala is necessary for a brief extinction deficit that follows fresh fear learning, a deficit thought to reflect the stress of learning itself.

Fear conditioning research also connects to symptoms. The hippocampus, amygdala and medial prefrontal cortex have been implicated in generating intrusive fear memories, and these regions largely overlap with known fear extinction pathways. Intrusions, in other words, may reflect the same circuitry that normally suppresses fear once it is no longer useful.

Roles of the amygdala, hippocampus and prefrontal cortex

The amygdala drives rapid threat detection and the physiological expression of fear. The hippocampus contributes to contextual and episodic memory, which helps explain why reminders tied to a particular place or situation can trigger symptoms. Both structures are involved in fear processing and in episodic and contextual learning, processes related to PTSD symptoms. The prefrontal cortex is thought to regulate this system. It is central to how fears are acquired and to the strategies used to reduce fear responses. Imaging studies commonly report reduced vmPFC activation and heightened amygdala activation in PTSD. A rodent study using light-based stimulation found that activating the vmPFC–amygdala pathway promoted the formation of extinction memory but not its retrieval. These findings suggest a plausible mechanism, though most of the causal evidence comes from animals.

Stress-response systems

The hypothalamic-pituitary-adrenal (HPA) axis is the central hormonal stress pathway, and its findings in PTSD are paradoxical. One of the earliest and most surprising biological findings was relatively low cortisol, in contrast to the elevated levels typically seen with acute and chronic stress. A meta-analysis of adult clinical samples found that morning and 24-hour cortisol were significantly lower in PTSD than in controls, though the effect sizes were small. Earlier pooled analyses of basal cortisol, however, found no systematic difference between people with current PTSD and comparison groups. Interpretations vary. One review proposes that enhanced negative feedback inhibition of the HPA axis, with reduced circulating cortisol and increased CRH, characterises PTSD, which contrasts with the hypercortisolemia seen in some anxiety disorders.

Noradrenergic signalling, mediated by the locus coeruleus, is closely tied to arousal, vigilance and the hyperarousal cluster of symptoms. Peripheral measurements have been inconsistent; one small study of recent-onset PTSD reported decreased serotonin, cortisol and noradrenaline alongside elevated IL-12 relative to controls. Serotonergic and glutamatergic pathways are also implicated. Serotonin modulates amygdala and prefrontal activity, which partly explains why serotonergic drugs are used clinically, while glutamate acting through NMDA receptors is required for the synaptic plasticity underlying fear memory consolidation and extinction. These mechanisms are better supported by pharmacological and animal studies than by large human biomarker studies.

Structural and functional brain findings

Structural imaging has produced the most consistent human data. The ENIGMA-PGC PTSD working group analysed neuroimaging and clinical data from 1868 subjects, 794 of them with PTSD, contributed by 16 cohorts. The group found significantly smaller hippocampi in subjects with current PTSD compared with trauma-exposed control subjects (Cohen's d = -0.17). The amygdala difference was smaller (d = -0.11), and it did not survive correction for multiple subcortical comparisons. Earlier meta-analyses were less uniform. Evidence on amygdala volume was described as even more equivocal, with studies reporting both smaller and larger volumes. A later meta-analysis found that the association with amygdala volume was partly due to confounding with trauma exposure.

The causal status of these differences remains uncertain. Most studies are cross-sectional, so they cannot show whether smaller hippocampal volume predates trauma and raises vulnerability, or results from trauma, stress hormones or chronic illness. Confounding by trauma exposure, comorbid depression and medication effects complicates interpretation, and the effect sizes are modest.

Genetic, epigenetic and gene-environment contributions

Twin and family studies indicate that PTSD has a heritable component, but no single gene has been established as a reliable determinant. Candidate-gene studies, including work on genes regulating glucocorticoid signalling, have had mixed replication, and large-scale genetic studies have so far explained only a small part of the risk. Epigenetic work is more mechanistic but largely comes from animal models. In one rodent model, fear learning increased acetylation of histones H3 and H4 in the prelimbic cortex and amygdala. Extinction learning, by contrast, increased H4 acetylation only in the infralimbic cortex, which suggests that histone modification (see epigenetics) may be specific to different stages of fear learning.

Gene-environment interaction is the most plausible framework for individual vulnerability. Genetic scores predicting hippocampal volume have been studied alongside trauma and PTSD status. The interaction between hippocampal volume polygenic scores and PTSD on hippocampal volume warrants deeper consideration. Among controls, a positive association was found between hippocampal volume polygenic scores and hippocampal volume. Such results indicate that genetic predispositions and trauma exposure may act jointly on the same brain structures, though the direction and mechanism of these effects are still being clarified. Neuroplasticity processes such as synaptic remodelling (see synapse and neuroplasticity) are the likely channel through which experience and genes meet, but direct human evidence on this point is limited.

Assessment and Screening

Structured interviews and self-report scales

Clinicians and researchers use two broad families of instruments. The Clinician-Administered PTSD Scale (CAPS-5) is a clinician-led interview that serves as the reference point for diagnosis. It is a 30-item structured interview that can establish a current diagnosis based on the past month, and it can also support a lifetime diagnosis or track symptoms over the past week. Its structure follows the DSM-5 clusters, and B, C, D and E symptoms are each rated for both frequency and intensity, with the ratings summed to produce severity scores. Scoring relies on a single index stressor: the interview asks about symptoms in relation to a single traumatic stressor over a 1-month period.

The PTSD Checklist for DSM-5 (PCL-5) is the most widely used self-report counterpart. Respondents indicate how much each problem has bothered them over the past month on a five-point scale, and the 20 items yield a total between 0 and 80. Because it requires no trained interviewer, it suits repeated measurement in clinics and trials, but it captures the respondent's own appraisal rather than a clinical judgement of symptom criteria.

Screening versus diagnosis

A high self-report total is a signal for further assessment, not a diagnosis in itself. For the PCL-5, two routes to a provisional diagnosis exist: a total score cutoff, or a symptom-pattern algorithm that requires at least one B item, one C item, two D items and two E items each endorsed at a rating of 2 or above. The German validation work illustrates how unstable cutoffs can be. Its authors found that a cutoff of 34 was most suitable for clinical use, while 38 was preferred for prevalence estimation, and that the originally proposed 31–33 range yielded acceptable to excellent diagnostic utility parameters but was not identified as optimal for any specific purpose. A meta-analysis of validation studies similarly reported that cutoffs range from 22 to 49. Against the CAPS-5, the item-pattern rule showed moderate agreement, with sensitivity of .81 and specificity of .71 in one study, leading its authors to conclude that the measure could serve as a screening tool while comparison with the gold standard from a structured clinical interview still needs testing in additional samples. In research, cutoffs are therefore best treated as cutoff-dependent estimates whose meaning shifts with the population, setting and purpose of the study, and in clinical settings they should prompt a structured interview rather than replace one.

Measurement consequences of DSM-5-TR and ICD-11

The two systems do not simply relabel the same symptoms; they change who is counted. ICD-11 focuses on the few symptoms considered central to PTSD, whereas the DSM-5 criteria include more symptoms and place greater emphasis on heterogeneous presentations. The DSM-5 also includes a negative cognition and mood cluster that the ICD-11 model omits, so the two instruments measure partly different constructs.

These differences are most pronounced in children. Versions of the DSM-5 criteria adapted for children aged six and younger place less emphasis on internalized, cognitively-sophisticated symptoms and instead highlight externalized, behaviorally-focused symptoms. In a 2025 comparison among children and adolescents, DSM-5 PTSD was significantly more common than ICD-11 PTSD (55.9% vs 33.2%), and the authors noted that the significant disparity in diagnosis rates between the two manuals appears primarily in the re-experiencing criterion. Agreement between the systems is often modest. Other studies, however, find no significant difference: in a sample of young children, the DSM-5 cutoff identified 19% of the sample with PTSD, against 11% under the ICD-11 measure, a gap the authors reported as not statistically significant. Discrepancies across studies therefore seem to depend partly on the measures and thresholds chosen. One study concluded that the differences largely reflected symptom thresholds used by the two measures. Because the choice of manual can change which children are identified, and so who receives evidence-based care, assessors should state explicitly which system and instrument they used.

Documenting trauma history and exposure

Any PTSD assessment depends on first establishing an index event. Practitioners should record the type of event, whether the person experienced it directly, witnessed it, or learned that a close person had been harmed, and the date on which it occurred. The time elapsed since the event matters, because it determines whether symptoms are assessed over the past month, as in the CAPS-5 and PCL-5, or over a lifetime. When someone has been exposed to several traumas, the rater should specify which event the symptom ratings refer to, since the answers may otherwise blend different experiences. Written documentation of these details supports later comparison across studies and across time, and it helps distinguish PTSD from other responses to adversity described in the differential diagnosis section.

Psychological Treatments

Trauma-focused psychotherapy is the central element of PTSD care in current clinical guidelines. The leading approaches share a common logic: they help patients engage with trauma memories, reminders and beliefs that the brain has linked to threat, rather than continuing to avoid them.

First-line trauma-focused therapies

Prolonged exposure (PE) involves repeated, structured revisiting of the traumatic memory in imagination and gradual return to situations that have been avoided. Prolonged exposure is among the most extensively tested PTSD treatments. Cognitive processing therapy (CPT) focuses on the self-blame, sense of permanent danger and other beliefs that patients build around the event, and it can be delivered with or without a written trauma account. Cognitive therapy, in the form developed by Ehlers and Clark, targets how the memory was poorly integrated and how current threat is appraised. Eye movement desensitization and reprocessing (EMDR) pairs recall of the memory with bilateral stimulation such as guided eye movements, although its proposed mechanism remains disputed. Trauma-focused cognitive behavioral therapy (TF-CBT) combines exposure, cognitive work and skills training, and was developed mainly for children but is also used with adults. Written exposure therapy (WET) is a brief approach in which patients write about the event over a small number of sessions.

Guideline recommendations

The major guidelines broadly agree on the primacy of psychotherapy but differ in how they rank individual treatments. The 2023 VA/DoD guideline recommends Cognitive Processing Therapy (CPT), Eye Movement Desensitization and Reprocessing (EMDR), and Prolonged Exposure (PE). When both treatment methods are available and feasible, the CPG recommends the psychotherapies over the pharmacotherapies, and the stated basis is larger and more persistent improvement with the former. Lower-strength suggestions include Ehler's cognitive therapy, Present-Centered Therapy (PCT), Written Exposure Therapy (WET) and Mindfulness-Based Stress Reduction (MBSR). The guideline's algorithm directs clinicians to begin by considering one of the three recommended trauma-focused psychotherapies but shift to medication or one of the suggested treatments based on patient preference or treatment availability. Its methods have been challenged: critics noted that some therapies were downgraded, and the evidence on trauma-focused psychotherapies was reviewed for each treatment individually, rather than as a class, for comparison with medications.

The 2018 ISTSS guidelines were built on a much larger evidence base, with 361 randomized controlled trials included, and two hundred and eight meta-analyses conducted and used to generate 125 recommendations. For treatment in the first three months after trauma, ISTSS recommended CBT-T, cognitive therapy and EMDR. The 2025 APA guideline is an update of its 2017 version and draws from 15 systematic reviews of interventions, where the earlier version relied on one. It lists cognitive processing therapy (CPT), prolonged exposure (PE) and trauma-focused cognitive behavioral therapy (TF-CBT) as first-line psychological treatment approaches. Eye movement desensitization and reprocessing (EMDR) therapy is listed as a second-line treatment. The divergence over EMDR's rank is a clear example of how guideline outcomes depend on the evidence threshold and the way studies are weighted.

Comparative effectiveness

Head-to-head trials of the leading trauma-focused therapies generally find broadly similar symptom reduction by the end of treatment, so the choice among them is often guided by patient preference, therapist expertise and local availability. Psychotherapy's advantage over medication is more contested over the long term. The VA/DoD rationale refers to more persistent improvement, but the size of the difference varies across analyses, and results depend on how outcomes such as remission, symptom severity and dropout are defined. Dose also matters: psychotherapies require an adequate dosage to be fully effective in reducing PTSD symptoms, and initial treatment effects will be noticeable after 4–8 sessions, which the guideline describes as generally accepted.

Barriers to access and retention

Several practical obstacles limit how far these treatments reach. Protocols such as PE, CPT and EMDR generally require specialized training and supervision, and therapist shortages are common in many health systems. A typical course spans roughly 8 to 15 sessions, which can be difficult for patients with work, caregiving or financial constraints. Not all patients respond fully, and a meaningful proportion do not reach remission, which is one reason guidelines emphasize tailoring. Dropout is another concern: in many trials and clinical settings, a notable share of patients leave treatment early, and this reduces the effective benefit of an otherwise efficacious therapy. Access problems also arise in primary care. A VA study protocol observed that the current VA/DOD clinical practice guidelines for management of PTSD in PC limit intervention options to prescription of antidepressant medication, supportive counseling, and referral to specialty care, and that these narrow treatment options often result in a majority of those Veterans who screen positive never receiving the most effective available care.

Pharmacological and Emerging Treatments

First-line medications

Selective serotonin reuptake inhibitors (SSRIs) and serotonin–norepinephrine reuptake inhibitors (SNRIs) form the main drug class for PTSD. The evidence base for PTSD psychopharmacology is strongest for sertraline, paroxetine and fluoxetine, along with the SNRI venlafaxine. Only the first two carry US Food and Drug Administration (FDA) approval for PTSD; from the FDA's perspective, all other uses are "off label," though the level of supporting evidence varies. Some secondary articles list fluoxetine and venlafaxine as FDA-approved as well, so the regulatory status of these agents is not described uniformly in the literature.

Efficacy against placebo is established but modest. Multisite randomized trials of sertraline and paroxetine found significant symptom reduction versus placebo, with remission in about 30% of participants. Response rates across studies vary from a low of 24.3% to a high of 60%. The sertraline evidence is also uneven: two of the four US registrational trials were negative on the primary efficacy endpoint. One review argues that these drugs mainly ease co-occurring depressive and anxious symptoms rather than producing lasting remission.

Why many patients respond only partially

Response heterogeneity is a central problem. A latent-class analysis of SSRI-treated patients identified fast responders, responders with low pretreatment symptom severity, and responders with high pretreatment symptom severity. Clinical moderators also matter: gender, sexual assault as the index trauma, and childhood sexual trauma showed univariate moderating effects on treatment response. These findings suggest that a single drug class cannot reach every patient, and that comorbidity and trauma history shape the outcome.

Off-label and adjunctive agents

Prazosin, an alpha-1 adrenergic antagonist, is the most studied non-SSRI agent for PTSD, mainly for nightmares. Apart from prazosin, there is little evidence for antiadrenergic agents as monotherapy or for preventing PTSD. In an early clinical series of combat veterans from Operation Iraqi Freedom, prazosin markedly reduced or eliminated trauma-related nightmares and sleep disruption in 23 of 25 returnees. That series was uncontrolled, and a placebo-controlled comparison with paroxetine was subsequently designed to test the effect more rigorously.

Atypical antipsychotics are used mainly as add-on therapy. They are used to reduce reexperiencing symptoms and nightmares, and are best used as adjunctive therapy to SSRIs. A meta-analysis found that SSRIs and atypical antipsychotics had significant efficacy compared with placebo, including in patients with severe PTSD. Adjunctive trials are not always straightforward; a phase 3 trial of brexpiprazole added to paroxetine or sertraline was terminated early due to challenges with patient eligibility, not safety concerns. Mood stabilizers and anticonvulsants have weaker support. One review noted that anticonvulsants, benzodiazepines, and atypical antipsychotics were not recommended at that time. Medication use also carries risk: a systematic review found that medicine interventions carried a higher risk of adverse effects than placebo.

Ketamine

Ketamine is a glutamatergic NMDA receptor antagonist. A randomized trial of a single intravenous infusion compared with midazolam found a significant and rapid reduction in PTSD symptom severity at 24 hours after infusion. A later randomized trial tested repeated infusions in chronic PTSD. Sixty-seven percent of participants in the ketamine group were treatment responders, compared with 20% in the midazolam group. Benefits did not last: among ketamine responders, the median time to loss of response was 27.5 days after the two-week course. The samples were small, so these findings remain preliminary.

MDMA-assisted therapy

The FDA granted breakthrough therapy designation for MDMA-assisted psychotherapy for PTSD on August 16, 2017. In this treatment, MDMA is given alongside psychotherapy in up to three monthly eight-hour sessions. The regulatory path stalled in 2024. An FDA advisory committee voted overwhelmingly against the idea that the clinical trials had proved MDMA effective for PTSD. The panel also voted 1-10 that the benefits did not outweigh the risks under the proposed risk evaluation and mitigation strategy. Concerns included potential bias from participants' prior MDMA use, unblinding, therapy misconduct, and inadequate side-effect reporting. In August 2024 the FDA issued a complete response letter declining the application. Regulators requested that the sponsor conduct an additional Phase 3 trial. A later resubmission has been reported, with additional analyses intended to address blinding and bias concerns; this report comes from a commercial website, and its status should be checked against FDA records.

Other investigational approaches

D-cycloserine, a partial NMDA agonist, has been tested as an adjunct to exposure therapy on the premise that it may strengthen fear-extinction learning. Its results in PTSD have been inconsistent, and it is not an established treatment. Virtual reality exposure places patients in simulated trauma-related environments. Small trials, particularly in veterans, have reported benefits comparable to conventional exposure, but larger comparative studies are still limited. None of these approaches has a settled place in guidelines, and the evidence for each remains provisional.

Special Populations

Children and adolescents

Which diagnostic system is applied can change how many young people are counted as having PTSD. In a study of children and adolescents, DSM-5 flagged about 56% as probably meeting PTSD criteria, against about 33% under ICD-11, and the authors tied much of the gap to the re-experiencing items which seems to be particularly related to the re-experiencing criterion. The two systems agreed only modestly in that sample, at a weak agreement of 74.5% between the two diagnoses manuals (kappa = .51). A separate sample of trauma-exposed youth showed the same direction of difference, with DSM-5 at 25.7% and ICD-11 at 16.0%, and adding extra re-experiencing items narrowed the gap PTSD was more prevalent using the DSM-5 criteria (25.7%) compared to the ICD-11 criteria (16.0%), with moderate agreement between these diagnostic systems, κ = .57. The inclusion of additional reexperiencing symptoms (i.e., ICD-11+) reduced this discrepancy in prevalence (24.7%).

Evidence for preadolescents is thinner. In one study of 7- to 11-year-olds, eight months after a hurricane, ICD-11 had the best-fitting model, followed by DSM-IV and DSM-5, and children who met DSM-5 criteria alone reported more depression and generalized anxiety. The authors concluded that use of only one model of PTSD, be it DSM-5 or ICD-11, will likely miss children with significant post-traumatic stress. By contrast, a study of Chinese adolescents found no significant PTSD prevalence differences between ICD-11 and DSM-5, so the divergence in youth is not uniform across samples.

Military personnel and veterans

Prevalence estimates for veterans vary with the population studied. One summary cites roughly 25% in combat-exposed military veterans, while a trial report gives between 10.1% and 30.9% of U.S. military Veterans. A Frontiers article reports a broader range for military members of 3 and 17%, which reflects differences in sampling, diagnostic method and time since deployment.

Treatment response is another concern. Veterans are benefit significantly less than non-military populations, according to one review, and in patients with chronic, complex presentations, non-response or partial response to medication is comparable or worse to those of the civilian patient population. Comorbidity is also common, with around 80% of those with a diagnosis of PTSD also meets criteria for another mental health condition. Research on complex PTSD in this group is small and heterogeneous; one systematic review found that prevalence of CPTSD ranged from 5% to 80.63%, while prevalence of PTSD ranged from 3.8% to 42.37%, and it could not pool the studies.

Healthcare workers and the general public during COVID-19

Pandemic-era studies of health workers produced high but widely varying estimates. A systematic review of 65 studies involving 97,333 health care workers across 21 countries reported a pooled PTSD prevalence of 21.5%, but its confidence interval ran from 10.5%-34.9%. A larger preprint covering 308 studies representing over 370,000 HCWs from 60 countries gave a pooled figure of 27.2%. Other syntheses are lower: an umbrella review that included only seven studies gave 13.52%. Rates appear to have moved over time. In the preprint, prevalence was significantly higher after the onset of COVID-19 (27.8%) compared to the pre-pandemic period (20.2%), and the increase was largest among staff exposed to mass casualty incidents. One analysis also linked the arrival of COVID vaccines to a sharp decline in the prevalence of PTSD.

For comparison, one review put the regular-times baseline for anxiety including PTSD in the general population at 3.6%, but that category is not directly equivalent to PTSD. Population surveys during the pandemic used different instruments and cut-off scores, which makes direct comparison between countries and studies difficult.

First responders, refugees and conflict-affected populations

For refugees, the figures reported in the sources I could access are wide-ranging. One secondary summary cites as high as 86% among certain refugee groups, but the group-specific basis for that number is not given, so it should be read as an upper bound rather than a typical value. Reliable statements about age and sex patterns in refugee and conflict-affected populations require population-level studies using comparable measures, and the sources I could verify do not provide them, so they are not summarised here.

First responders such as police officers, firefighters and paramedics are repeatedly exposed to death, injury and violence, which makes them a group of concern. I was unable to verify pooled prevalence estimates for this group, and no figures are presented here.

Historical Development of the Concept

Earlier descriptions and shifting names

Psychological harm from war was described long before PTSD existed as a diagnosis. Trauma-related symptoms among veterans of military engagement have been documented at least since the time of the ancient Greeks, with modern names including shell shock, battle fatigue, and Post Traumatic Stress Disorder. Nineteenth-century American clinicians described soldiers whose heart palpitations were labelled soldier heart, and in the Civil War era soldiers and military physicians talked about wartime ailments known as "nostalgia" and "soldier's heart."

The First World War produced the term that is most closely associated with the condition. Shell shock was poorly defined from the start: cases could be interpreted as either a physical or psychological injury. The psychologist Charles Myers introduced the term into medical writing in 1915, and he argued that the condition was psychological rather than purely physical. In the Second World War, clinicians used labels such as "battle shock," "psychiatric collapse," "combat fatigue," and "war neurosis". A recurring pattern is that a new name tends to appear after major wars end, replacing its predecessor. A study of newspaper archives found that this pattern repeated across the twentieth century, which the authors argued could hinder clinical and scientific progress.

From DSM-I to DSM-III

The American Psychiatric Association's first manual, DSM-I (1952), used the category "gross stress reaction" for the symptoms that followed trauma. DSM-II (1968) dropped this category, a decision that was not well explained, and soldiers returning from Vietnam organized and clamored for a diagnosis recognizing the psychological impact of war. Veterans' counselors took their case to the chair of the task force revising the manual and asked for a post-Vietnam syndrome entry. The diagnosis was added in DSM-III in 1980. Its trauma criterion required an event "outside the range of usual human experience", and the activist origin of the diagnosis is still discussed: the impetus came not from scientists and clinicians but from activists, many of them Vietnam veterans.

Later revisions changed the criteria considerably. DSM-III-R (1987), DSM-IV (1994) and DSM-5 (2013) continued to reflect an evolving understanding of how the condition affects a person's daily life and their ability to function on a long-term basis. DSM-5 moved PTSD out of the anxiety chapter into a new category of trauma- and stressor-related disorders, and it expanded the symptom list, a rise from 17 to 20 compared with DSM-IV. The trauma criterion was narrowed in DSM-5: the subjective-response requirement of DSM-IV was removed, and the qualifying event was limited to actual or threatened death, serious injury, or sexual violence.

Divergence from ICD-10 and the emergence of complex PTSD

Early comparisons suggested that the two international systems would converge. Critics later described the differences between ICD-10 and DSM-IV as "definitional differences without an apparent conceptual basis". The divergence came with the proposed ICD-11 version. Judith Herman first proposed a complex form of the disorder in 1992, drawing on survivors of prolonged, repeated trauma, and the concept was reflected in DSM-IV's proposed category of Disorders of Extreme Stress, which was not adopted. The World Health Organization proposed the inclusion of complex PTSD as a new diagnosis that is related to, but separate from, PTSD. The DSM-5 working group reviewed the evidence and concluded that there is not enough empirical support for a distinct disorder, so the ICD-11 model became a separate category while DSM-5 expanded PTSD to include some of its features. The complex PTSD debate is treated in detail elsewhere in this entry.

Continuing debates

Several questions remain open. The first concerns the breadth of the trauma definition, since critics such as McNally have argued that the definition of trauma is so broad that the PTSD diagnosis has lost specificity. The second concerns the latent structure of symptoms, and whether complex presentations form a distinct condition or a more severe form of PTSD. Authors reviewing the two systems have noted that ICD-11 creates a dichotomy but the criteria themselves suggest a difference in severity rather than category. The third concerns whether the two manuals describe the same condition at all. The historical record shows that the concept was shaped by veterans' advocacy, by clinical experience with civilian trauma, and by political and institutional negotiation, and those influences continue to affect how the boundaries of the diagnosis are drawn.

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