Little is known about the prevalence of mental health outcomes in UK personnel at the end of the British involvement in the Iraq and Afghanistan conflicts.

We examined the prevalence of mental disorders and alcohol misuse, whether this differed between serving and ex-serving regular personnel and by deployment status.

This is the third phase of a military cohort study (2014–2016; n = 8093). The sample was based on participants from previous phases (2004–2006 and 2007–2009) and a new randomly selected sample of those who had joined the UK armed forces since 2009.

The prevalence was 6.2% for probable post-traumatic stress disorder, 21.9% for common mental disorders and 10.0% for alcohol misuse. Deployment to Iraq or Afghanistan and a combat role during deployment were associated with significantly worse mental health outcomes and alcohol misuse in ex-serving regular personnel but not in currently serving regular personnel.

The findings highlight an increasing prevalence of post-traumatic stress disorder and a lowering prevalence of alcohol misuse compared with our previous findings and stresses the importance of continued surveillance during service and beyond.

All authors are based at King's College London which, for the purpose of this study and other military-related studies, receives funding from the UK Ministry of Defence (MoD). S.A.M.S., M.J., L.H., D.P., S.M. and R.J.R. salaries were totally or partially paid by the UK MoD. The UK MoD provides support to the Academic Department of Military Mental Health, and the salaries of N.J., N.G. and N.T.F. are covered totally or partly by this contribution. D.Mu. is employed by Combat Stress, a national UK charity that provides clinical mental health services to veterans. D.MacM. is the lead consultant for an NHS Veteran Mental Health Service. N.G. is the Royal College of Psychiatrists’ Lead for Military and Veterans’ Health, a trustee of Walking with the Wounded, and an independent director at the Forces in Mind Trust; however, he was not directed by these organisations in any way in relation to his contribution to this paper. N.J. is a full-time member of the armed forces seconded to King's College London. N.T.F. reports grants from the US Department of Defense and the UK MoD, is a trustee (unpaid) of The Warrior Programme and an independent advisor to the Independent Group Advising on the Release of Data (IGARD). S.W. is a trustee (unpaid) of Combat Stress and Honorary Civilian Consultant Advisor in Psychiatry for the British Army (unpaid). S.W. is affiliated to the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Emergency Preparedness and Response at King's College London in partnership with Public Health England, in collaboration with the University of East Anglia and Newcastle University. The views expressed are those of the author(s) and not necessarily those of the National Health Service, the NIHR, the Department of Health, Public Health England or the UK MoD.

For armed forces personnel, data on help-seeking behaviour and receipt of treatment for mental disorders are important for both research and policy.

To examine mental healthcare service use and receipt of treatment in a sample of the UK military.

Participants were drawn from an existing UK military health cohort. The sample was stratified by reserve status and by participation in the main war-fighting period of the Iraq War. Participants completed a telephone-based structured diagnostic interview comprising the Patient Health Questionnaire and Primary Care Post-Traumatic Stress Disorder Screen (PC–PTSD), and a series of questions about service utilisation and treatment receipt.

Only 23% of those with common mental disorders and still serving in the military were receiving any form of medical professional help. Non-medical sources of help such as chaplains were more widely used. Among regular personnel in receipt of professional help, most were seen in primary care (79%) and the most common treatment was medication or counselling/psychotherapy. Few regular personnel were receiving cognitive–behavioural therapy (CBT). These findings are comparable with those reported for the general population.

In the UK armed forces, the majority of those with mental disorders are not currently seeking medical help for their symptoms. Further work to understand barriers to care is important and timely given that this is a group at risk of occupational psychiatric injury.

Deployment to the 2003 Iraq War was associated with ill health in reserve armed forces personnel.

To investigate reasons for the excess of ill health in reservists.

UK personnel who were deployed to the 2003 Iraq War completed a health survey about experiences on deployment to Iraq. Health status was measured using self-report of common mental disorders, post-traumatic stress disorder (PTSD), fatigue, physical symptoms and well-being.

Reservists were older and of higher rank than the regular forces. They reported higher exposure to traumatic experiences, lower unit cohesion, more problems adjusting to homecoming and lower marital satisfaction. Most health outcomes could be explained by role, experience of traumatic events or unit cohesion in theatre. PTSD symptoms were the one exception and were paradoxically most powerfully affected by differences in problems at home rather than events in Iraq.

The increased ill-health of reservists appears to be due to experiences on deployment and difficulties with homecoming.