Combat Exposure and PTSD: What the Research Says About Complex Trauma in Veterans

Combat exposure raises the risk of PTSD and complex PTSD (CPTSD) in veterans, and the research shows the link is strongest for the complex form. Most exposed people do not develop either. In the latest UK cohort survey, ex-serving personnel whose last Iraq or Afghanistan deployment was in a combat role had about twice the odds of CPTSD of those in other roles. A Danish study of treatment-seeking veterans found combat exposure, more time since the trauma and being single all marked out CPTSD. These are population findings and do not predict what happens to any one person.

What the UK cohort shows

The King's College London Centre for Military Health Research (KCMHR) Phase 4 report surveyed 4,104 serving and ex-serving UK personnel between January 2022 and September 2023. Participants had served during the Iraq and Afghanistan conflicts, and the study has followed this group since 2004. A 2026 paper by Sharp and colleagues in Occupational and Environmental Medicine reports the main results.

The report and the paper give slightly different rounded figures for PTSD, so the table shows both ends. The comparison group in each row is personnel whose last deployment was in a non-combat role. KCMHR also reports that 13.9% of ex-serving personnel who deployed in a combat role met CPTSD criteria, against 7.1% of serving personnel in combat roles.

Deployment on its own told a different story for serving and ex-serving groups. Among ex-serving regulars, 12.6% of those who deployed to Iraq or Afghanistan met PTSD criteria against 7.6% of those who did not. For CPTSD the split was 8.6% against 3.7%. Among serving regulars the report found no significant difference. The authors of the paper conclude that combat deployment has an enduring impact on PTSD.

What the Danish study adds

Folke and colleagues studied 599 previously deployed Danish soldiers and veterans seeking treatment, and published in the Journal of Psychiatric Research in 2023. In that group 13.0% met probable ICD-11 PTSD criteria and 31.4% met probable CPTSD criteria. Compared with people with no trauma disorder, the risk factors for CPTSD were:

• Exposure to warfare or combat.
• A longer time since the traumatic event.
• Being single.

People with CPTSD in this sample reported more depression, anxiety and stress, more psychotropic medication use and more suicide attempts than people with PTSD alone. The authors call CPTSD more common and more debilitating than PTSD in treatment-seeking soldiers and veterans. Because the sample came from a military psychology department, the figures describe people who sought help and do not give a rate for all Danish veterans.

Combat is one route among several

Three points keep the findings in proportion.

• Most veterans do not develop PTSD. KCMHR found probable PTSD in 9.4% of its 2022 to 2023 sample, and the VA Center for PTSD reports a lifetime rate of 29% for Iraq and Afghanistan era US veterans and 10% for Vietnam veterans.
• Roughly 28.5% of the UK cohort's PTSD cases were in people who never deployed to Iraq or Afghanistan, according to a post-hoc analysis in the KCMHR report. Training accidents, bereavement, childhood experiences and other events also lead to PTSD.
• The studies are cross-sectional or observational. They show associations and do not test why combat exposure matters.

Rates have also risen over time in the UK cohort. KCMHR reports probable PTSD of 4% in 2004 to 2006, 6.2% in 2014 to 2016 and 9.9% in 2022 to 2023 on the same checklist. Ex-serving personnel had higher rates than serving personnel in the latest survey: 10.5% against 7.4% for PTSD and 6.5% against 3.9% for CPTSD.

Why time since the event matters

The Danish finding on time since the trauma means CPTSD is more common among people whose trauma lies further in the past. The study design cannot show whether symptoms deepen over time, whether people with more severe symptoms keep seeking help for longer, or whether both apply. The NICE guideline context states that PTSD is treatable even when diagnosed years later, that symptoms begin late in a minority of cases, and that people may not seek help for months or years.

The size of that delay shows up in US research on deployed troops. In a 2004 study in the New England Journal of Medicine, Hoge and colleagues surveyed US soldiers and Marines three to four months after return. Between 15.6% and 17.1% of those back from Iraq screened positive for depression, anxiety or PTSD, against 9.3% before deployment. Only 23% to 40% of those who screened positive sought mental health care, and they were about twice as likely as others to cite stigma and other barriers.

What helps, according to the guidelines

Treatment for combat-related PTSD follows the same guidelines as other PTSD. The VA/DoD guideline (Version 4.0, 2023) strongly recommends individual trauma-focused therapy: cognitive processing therapy, prolonged exposure or EMDR. NICE (2018) recommends individual trauma-focused CBT for adults. A 2025 review by Billings and Nicholls reports that NICE supports EMDR where the person prefers it and excludes combat-related trauma from that support. Ask a clinician which approach applies to your circumstances.

Social connection forms part of the research picture too. KCMHR found that ex-serving personnel who reported poor social support had higher rates of PTSD and CPTSD, which our article on isolation and trauma covers in detail. For the difference between the two diagnoses, see PTSD vs complex PTSD.

Where to get help

• England: Op COURAGE, the NHS Veterans Mental Health and Wellbeing Service, accepts self-referral and referral from a GP or charity. Eligibility: resident in England, served at least one full day in the UK Armed Forces, and registered with or eligible to register with an English GP. Regional numbers are on the NHS veterans mental health page.
• UK-wide: Combat Stress helps veterans and families on its free 24-hour helpline, 0800 138 1619.
• US: contact your local VA facility or Vet Center to ask about trauma-focused therapy. The Vet Center combat call line, 1-877-927-8387, connects you with another combat veteran.