Dual use of alcohol and marijuana and condomless sex in young adult men and women: A within-subject day-level analysis.

BACKGROUND AND OBJECTIVES: Unprotected sex has been linked independently to alcohol and marijuana use, but few studies have examined associations with dual use or gender differences in these associations.

METHODS: This study examined day-level associations between unprotected sex, defined as condomless vaginal sex with an opposite-sex partner, and use of alcohol, marijuana, neither, or both substances among 290 young adults (18-25 years, 52.3% female) who reported either alcohol or marijuana use. Participants reported demographics, alcohol use, marijuana use, and at least one episode of condomless sex as defined above in the past 90 days (Timeline Follow-Back). The likelihood of condomless sex was examined for days when alcohol, marijuana, neither, or both were used. Gender differences were also explored.

RESULTS: For females, compared to days with no substance use, the estimated risk of condomless sex increased by a factor of 2.12 on alcohol use days, 1.89 on marijuana use days, and 3.39 on dual use days. Among males, the odds of condomless sex increased only slightly on alcohol use (odds ratio [OR] = 1.03) or marijuana use (OR = 1.08) days, but increased by a factor of 1.71 on dual use days.

DISCUSSION AND CONCLUSIONS: Young persons who use alcohol and/or marijuana experience heightened likelihood of condomless sex. This increased likelihood is greater for women than for men on days with alcohol or marijuana use, each alone but especially when combined.

SCIENTIFIC SIGNIFICANCE: Young women may be especially susceptible to the influence of alcohol and/or marijuana use on sexual behavior. (Am J Addict 2018;XX:1-6).