Event-Level Associations of Marijuana and Heavy Alcohol Use With Intercourse and Condom Use

The associations substance use has with sex and condom use among college students appear to be well documented and of clear public health significance. However, few event-level studies examine marijuana or heavy alcohol use, control for temporal patterns shared among these behaviors, or consider differences by relationship status. We recruited 284 18- to 22-year-old undergraduate men and women (79%), 61% of whom were in a serious relationship. For 24 consecutive days, participants reported on their prior day marijuana use, heavy alcohol use, vaginal intercourse, and condom use. Most intercourse events (86%) were reported by participants in a serious relationship, and most (62%) were not protected by a condom. Hierarchical generalized linear models indicated that participants in a serious relationship were more likely to report intercourse than were others. Adjusting for weekly patterns in intercourse, odds of intercourse were higher on days participants reported marijuana or heavy alcohol use; the latter effect was stronger for single participants. Being drunk during sex, being in a serious relationship, and using noncondom birth control were associated with less condom use. Models distinguish among multiple potential influences on undergraduates' sexual behavior. Findings suggest that greater attention to the relationship and other contexts of marijuana and alcohol use may be relevant to understanding young adults' sexual behavior and preventing health-risking or nonconsensual sex.