Aims
To determine the prevalence of comorbid probable post-traumatic stress disorder and alcohol misuse in a UK military cohort study and to determine the level of co-occurrence between these disorders; further aims were to investigate the association between alcohol misuse and the different PTSD symptom clusters, and to assess what factors are associated with probable PTSD in participants with alcohol misuse.

Methods
Data from 9984 participants of Phase 2 of the health and well-being survey of serving and ex-serving members of the UK Armed Forces were assessed for probable PTSD and alcohol misuse using the PTSD checklist (PCL-C) and the alcohol use disorders identification test (AUDIT), respectively.

Results
1.8 % [95 % confidence interval (CI) 1.5–2.1] of the sample met the criteria for both PTSD and alcohol misuse. All three symptom clusters of PTSD were significantly associated with alcohol misuse, with similar odds ranging from 2.46 to 2.85. Factors associated with probable PTSD in individuals reporting alcohol misuse were age [ages 30–34 (years): OR 2.51, 95 % CI 1.15–5.49; ages 40–44 years: OR 2.77, 95 % CI 1.18–6.47], officer rank (OR 0.36, 95 % CI 0.16–0.85), being in a combat role in parent unit (OR 1.99, 95 % CI 1.20–3.31) and common mental disorder (CMD) (OR 21.56, 95 % CI 12.00–38.74).

Conclusions
This study provides strong evidence that PTSD and alcohol misuse are often co-occurring. CMD was highly associated with probable PTSD in individuals with alcohol misuse.