Are military personnel with a past history of mental health care more vulnerable to the negative psychological effects of combat

Introduction: Military clinicians often need to assess fitness for duty after a mental disorder diagnosis. The ability to respond to the psychological demands of deployment is a primary consideration. This analysis explores whether personnel with past mental health problems are more vulnerable to the effects of combat. Methods: Data came from 16,944 Canadian Armed Forces personnel undergoing post-deployment screening in 2009–2012 after deployment in support of the mission in Afghanistan. Those who had previous deployments (n = 9,852) and those who were currently in mental health care (n = 588) were excluded, leaving 6,504 in the analysis sample. The primary outcomes were the presence of one or more of six common mental health problems assessed by the screening questionnaire and the SF-36 Health Survey Mental Component Summary (MCS), a dimensional measure of general mental health. Logistic and linear regression were used to assess the interaction between past mental health care (a proxy for past mental health) and a 30-item combat exposure scale. Results: Past mental health care and combat were strongly and independently associated with both primary outcomes, but no statistically significant interaction was seen for either. Discussion: The effects of past mental health and combat on post-deployment mental health are simply additive. Those with past mental health problems are not, on average, more vulnerable to the effects of combat. The variability in outcome at the individual level and the treatability of common mental disorders argue for an individualized approach to fitness-for-duty decisions.