Mechanisms of behavior change in a brief dual-target motivational intervention: Reduction in alcohol use mediates intervention effects on risky sex.

To examine the mechanisms underlying the efficacy of a dual-target motivational intervention (MI) to reduce heavy drinking and risky sex. A priori hypotheses were that: increases in alcohol-related readiness to change (RTC) and self-efficacy would mediate the effect of MI on alcohol use; increases in sex-related RTC and self-efficacy would mediate the effect of MI on risky sex; and reductions in alcohol use would mediate reductions in risky sex. Patients in Emergency Departments who screened positive for heavy drinking and risky sex were randomly assigned to receive MI or brief advice. RTC and self-efficacy were assessed at baseline and immediately postintervention. Alcohol use and sexual behavior was assessed at baseline, 3-, 6-, and 9-month follow up. Single-and serial-mediation models were tested. Patients who received MI had higher postintervention RTC and self-efficacy, but neither mechanism mediated the effects of MI on behavioral outcomes. Reduction in heavy drinking mediated the effect of MI on frequency of sex under the influence (SUI). Further, the effect of MI on condomless sex was mediated by an indirect path in which reductions in heavy drinking at 3 months predicted less SUI at 6 months, which in turn predicted reduction in condomless sex at 9-months. Although some effect of dual-target MI on risky sex is independent of drinking, treatment-related reduction in heavy drinking does account for a significant portion of reduction in risky sex, providing support for the utility of this intervention in patient populations where heavy drinking and risky sex co-occur.