A retrospective cohort analysis of risk of drug overdose deaths among US Vietnam War‐era veterans, 1979–2021

Background and aims Drug use among United States military veterans has clinical and public health implications. This study determined the risk of post‐military service drug overdose mortality (1979–2021) among all veterans who served in the military during the 1961–1975 Vietnam War‐era. Design, setting and participants This retrospective cohort study compared the risk of drug overdose mortality among all United States military veterans that served in Vietnam during the Vietnam War (theater veterans) to that of all veterans who served during the Vietnam War but not in Vietnam (non‐theater). This comprehensive population assessment included veterans born between 1900 and 1958, alive as of 1979 and with military service between 1961 and 1975. Participants included 9 496 285 Vietnam War‐era veterans (2 443 567 theater; 7 052 718 non‐theater). Measurements Mortality outcomes included all, accidental and intentional drug overdoses (1979–2021) and drug overdoses involving opioids and/or stimulants (1999–2021). Drug overdose mortality risks were assessed using Cox Proportional Hazards models that generated hazard ratios (HRs) and 95% confidence intervals (CIs) adjusted for covariates. Trends of overdose mortality rates over time for theater vs. non‐theater veterans were assessed by calculating average annual percent change (AAPC) in crude rates/100 000 persons (CRs). Results Average age at baseline approximately 33 years. Most veterans were male (~97%), Caucasian (>75%) and Army (~50%). There were 9148 theater veteran drug overdose deaths (CR = 10.01) and 33 322 among non‐theater veterans (CR = 12.87). Compared with non‐theater veterans, theater veterans had increased risks of all drug overdose mortality (HR = 1.03, P < 0.0001; 95% CI = 1.01–1.06) and accidental drug overdose mortality (6427; 23 347, respectively) (HR = 1.08, P < 0.0001; 95% CI = 1.05–1.12); risk of intentional drug overdose mortality was lower (1683; 6435, respectively) (HR = 0.90, P < 0.001; 95% CI = 0.85–0.95). Theater veterans had increased risk of accidental drug overdose deaths involving opioids without stimulants (HR = 1.10, P = 0.0005; 95% CI = 1.04–1.17), stimulants without opioids (HR = 1.20, P < 0.0001; 95% CI = 1.12–1.29) and opioids and/or stimulants (HR = 1.13, P < 0.0001; 95% CI = 1.08–1.17). CRs for all drug overdose mortality (1979–2021) increased for theater veterans (CR = 4.06, 1979; CR = 15.48, 2021; AAPC = 2.70, P < 0.001) and non‐theater veterans (CR = 4.32, 1979; CR = 24.05, 2021; AAPC = 3.94, P < 0.001). Theater and non‐theater veterans had increased CRs of overdose deaths (1999–2021) involving stimulants without opioids (AAPC = 5.30, P < 0.013 and AAPC = 6.28, P < 0.006, respectively). Summary United States military veterans who served in Vietnam during the Vietnam War have a small increased risk of drug overdose mortality compared with veterans who did not serve in Vietnam.