Alcohol and marijuana use during sex are associated with unprotected sex among MSM and MSMW

Background: We use data from the Chicago site of the NIDA Sexual Acquisition and Transmission of HIV – Cooperative Agreement Program to investigate how substance use at the time of sexual encounters may influence the likelihood of engaging in unprotected vaginal or anal sex among men who have sex with men (MSM). Methods: Respondent driven sampling was used to recruit hard drug users, MSM, and their sex partners. Analyses were restricted to 458 men who reported having sex with a man in the past six months; most were low-income men of color, and 73% also had a female partner. Respondents reported on the most recent sexual encounter with up to six partners (median=3). Substances commonly reported included alcohol, marijuana, crack, heroin, and speedball. Mixed effects logistic regression analyses were conducted to test the effects of substance use during sex on vaginal and anal sex without a condom. Results: Respondent's alcohol use (≥ 4 drinks) was associated with a 4-fold increased likelihood of unprotected vaginal sex. Alcohol use (≥ 4 drinks) by both the respondent and his female partner was associated with a 3-fold increased likelihood of unprotected anal sex. Marijuana use by both the respondent and his male partner was associated with an 8-fold increased risk of unprotected receptive anal sex. Conclusions: Alcohol use and marijuana use during sex contribute to an increased risk of unprotected sex among MSM. The use of illicit drugs other than marijuana during sex was not significantly associated with unprotected sex in this sample.