Nested Event-Level Case-Control Study of Drug Use and Sexual Outcomes in Multipartner Encounters Reported by Men Who Have Sex with Men.

Previous event-level analyses have often, but not always, found significant associations between drug use and sexual risk behaviour in men who have sex with men (MSM), but these analyses have rarely considered either multipartner encounters specifically, or other sexual outcomes such as pleasure and control. Using data from an internet-based longitudinal survey of MSM, we tested the association between drug use by respondent and by partners and unprotected anal intercourse (UAI), pleasure and control over sexual activity. Overall respondent substance use was significantly associated with increased odds of UAI, though not with pleasure or control. Respondent use of crystal methamphetamine was significantly associated with both increased odds of UAI and decreased odds of control over sexual activity. This analysis agrees with previous studies of dyadic encounters, and specifically suggests that the association between crystal methamphetamine and sexual risk behaviour may be mediated by loss of control.