Examining lifetime and current (6-month) prevalence of several psychiatric disorders in the NVVRS, Jordan et al. (1991) found significantly higher rates of alcohol and drug abuse or dependence in Vietnam-theater veterans (1200 men and 432 women) than in Vietnam-era veterans (412 men and 304 women) or civilian controls (450 men and 218 women). The most prevalent disorder among male veterans was alcohol abuse or dependence: 39.2% lifetime and 11.2% current for theater veterans and 37.9% lifetime and 9.2% current for era veterans. The prevalence of lifetime and current alcohol abuse or dependence in female theater veterans was 9.1% and 4.9%, respectively, and in female era veterans 4.2% and 1.1%, respectively. The prevalence of lifetime and current drug abuse or dependence was 5.7% and 1.8% in male theater veterans, respectively, and 5.3% and 1.0% in male era veterans. For women, the prevalence of lifetime and current drug abuse or dependence was 1.0% or less for all groups. However when the theater group was dichotomized by level of war-zone stress—high (406 men and 170 women) and low or moderate (783 men and 262 women)—the investigators found that the men and women exposed to high war-zone stress did have significantly higher rates of both lifetime and current alcohol and drug abuse or dependence than the other groups. The 6-month prevalence of alcohol disorders among men was 17.2% in the high group, 8.8% in the low or moderate group, 9.2% in the era controls, and 7.8% in the civilian sample, and 3.4%, 1.6%, 1.0%, and 0.9%, respectively, for women. The lifetime prevalence was 45.6%, 37.2%, 37.9%, and 27.1%, respectively, for men and 10.6%, 8.2%, 4.6%, and 1.5%, respectively, for women. For drug disorders, the current prevalence among men were 3.9%, 1.1%, 1.0%, 0.9%, respectively; the prevalence among female veterans was 0.0% for all groups. The lifetime prevalence of drug disorders was 8.4%, 4.9%, 6.0%, and 3.4%, respectively, for men, and 2.57%, 0.0%, 0.6%, and 0.9%, respectively, for women. Thus, an association of problems with substance use was demonstrated with exposure to combat stress, but not with deployment to a war zone.

Goldberg et al. (1990) used the Vietnam Era Twin Registry to assess alcohol-drinking patterns in Vietnam-theater veterans. They analyzed 2169 monozygotic twin pairs. Veterans who served in Vietnam had a higher consumption of alcohol than those who did not serve (17.0% vs 21.4%), and the degree of combat exposure was related to higher daily alcohol consumption. For example, the prevalence of high average daily consumption increased from 15.3% in theater veterans with no combat exposure, to 20.7%, 24.5% and 24.7% in veterans with low, medium, and high combat exposure, respectively (χ2 trend = 6.625, p = 0.010). The authors noted that they did not control for alcohol consumption before military service because of the potential for recall bias. McLeod et al. (2001) also used data from the Vietnam Era Twin Registry and found that combat exposure was associated with alcohol consumption.

Koenen et al. (2003a) also used telephone interview data from the 1993 Vietnam Era Twin Registry study to assess severity of combat exposure, alcohol consumption, and substance-use disorders in 1874 male-male monozygotic twin pairs. As in the NVVRS, severity of combat exposure was significantly associated with alcohol dependence (OR 1.16, 95% CI 1.02-1.31), drug dependence (OR 1.34, 95% CI 1.03-1.48), and cannabis dependence (OR 1.36, 95% CI 1.09-1.71). After adjustment for combat-related PTSD (diagnosed with the DIS-III-R), combat exposure was significantly associated only with alcohol dependence (OR 1.15, 95% CI 1.01-1.30) and cannabis dependence (OR 1.31, 95% CI 1.04-1.66).

In the Gulf War, stress appears to have increased the risk of substance-related conditions. In the large Iowa cohort of regular military, National Guard, and reservists surveyed by telephone in 1995-1996 (1896 deployed and 1799 nondeployed military personnel), the prevalence of symptoms of alcohol abuse as determined with CAGE was 17.0% and 19.4% in



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