Aggregate versus day level association between methamphetamine use and HIV medication non-adherence among gay and bisexual men.

Methamphetamine use is associated with HIV infection, especially among gay and bisexual men. Methamphetamine use contributes to disease progression both directly, by increasing viral load and damaging the immune system, and indirectly, by decreasing medication adherence. Research examining the association of methamphetamine use and non-adherence has traditionally compared groups of users and nonusers on adherence, compared methamphetamine use between participants above or below some threshold level of adherence (e.g. >90 % dose adherence), or examined aggregate relationships. Using Timeline Follow-back procedures, the present study examined aggregate, threshold, and day-level associations of methamphetamine use with non-adherence in 210 HIV-positive gay and bisexual methamphetamine-using men. Methamphetamine use was not associated with adherence behavior at the aggregate-level, but methamphetamine use on a given day was associated with 2.3 times the odds of non-adherence on that day. Threshold results were equivocal. These data suggest that the methamphetamine and non-adherence relationship is complicated: non-adherence is more likely to occur on days in which methamphetamine is used, but participants reported more non-adherence days in which methamphetamine was not used. This seeming paradox generates questions about the selection of analytical techniques and has important implications for behavioral interventions targeting substance use and adherence among HIV-positive individuals.