Objective. This study examined the association between event-level methamphetamine use and heterosexual risk behaviors. Methods. Data on 1213 heterosexual encounters were collected using audio-computer assisted self interviews from 703 injecting drug users in North Carolina. Data were obtained by asking participants a series of questions about the last time that they had sex (oral, vaginal, and/or anal). Although participants were interviewed at up to 3 time points, data were analyzed at the event level rather than as longitudinal because we were interested in the co-occurrence of methamphetamine use and sexual risk behaviors. Multivariate generalized estimating equations models were developed to examine the association between co-occurring methamphetamine use and each of 6 heterosexual risk behaviors. Results. Methamphetamine was used in 7% of encounters. Methamphetamine use by either or both partners was associated with an increased likelihood of anal intercourse (odds ratio [OR] = 2.41, 95% confidence interval [CI] = 1.29-4.53), vaginal and anal intercourse (OR = 2.41, 95% CI = 1.22-4.77), and sex with a new partner (OR = 1.98, 95% CI = 1.09-3.61). In addition to these behaviors, methamphetamine use by both partners was also significantly associated with unprotected intercourse with a new partner (OR = 5.20, 95% CI = 2.09-12.93) and unprotected anal intercourse (OR = 4.63, 95% CI = 1.69-12.70). Conclusions. Methamphetamine use during heterosexual encounters appears to increase sexual risk-taking, especially when both partners are using it.
