This study seeks to decrease methamphetamine use and concomitant high-risk sexual behaviors among methamphetamine-using men who have sex with men (MSM) by combining a biomedical intervention with a behavioral intervention. The behavioral intervention will consist of an 8-week course of contingency management (CM) through which participants will be reinforced for testing negative for methamphetamine metabolites during periodic urine analyses. The biomedical intervention involves a 28-day course of an antiretroviral drug (Truvada) to be administered after an unanticipated HIV risk exposure (i.e., engaging in either receptive or insertive anal sex without a condom with someone who is HIV-positive or of unknown status). In combining these two interventions, this study seeks to evaluate the combined intervention's effects on sexual risk behaviors and methamphetamine use.

At the baseline, all eligible participants underwent informed consent; completed baseline assessments; received rapid HIV testing; provided specimens for syphilis, gonorrhea and chlamydia testing; and received a medical examination. Those who reported a high-risk sexual or drug exposure episode with an HIV-positive or serostatus-unknown source within the preceding 72 hours immediately initiated postexposure prophylaxis. All other participants received a 4-day ''starter pack'' of Truvada to be initiated only in the case of a future high-risk exposure to HIV. All participants began the voucher-based CM intervention upon study entry. For the initial 8 weeks of study conduct, participants presented to the study site three times weekly for a urine drug screen for methamphetamine metabolites. Participants who provided urine samples that were negative for methamphetamine metabolites earned vouchers, which escalated in value for successive negative urine samples. A participant with a missing sample or a sample positive for methamphetamine metabolites did not earn vouchers. Accrued vouchers were never forfeited and could be redeemed at any time during the study for gift certificates or goods or services that promote healthy, pro-social behaviors; vouchers could not be redeemed for cash.

Inclusion Criteria:

• Individual must identify as a male who has sex with other men (MSM);
• At least 18 years of age;
• HIV negative serostatus on baseline rapid oral HIV antibody test;
• Self-reported methamphetamine use within the previous 72 hours and test positive for methamphetamine metabolites at baseline;
• Self-reported unprotected anal intercourse (either receptive or insertive) with an HIV-positive or status unknown partner within the previous 3 months;
• Self-reports no previous hypersensitivity to any of the components of Truvada (tenofovir disoproxil fumarate or emtricitabine);
• Willing to comply with study requirements (i.e., monitored urine testing three times per week, meet with physician within first week of enrollment, begin medication immediately following an unexpected high-risk sexual exposure, and contact the clinic and meet with physician within 92 hours of unexpected high-risk sexual exposure).

Exclusion Criteria:

• Does not identify as a male who has sex with other men;
• Under 18 years of age;
• HIV positive, by self-report or as indicated by the results on the baseline rapid oral HIV antibody test;
• Self-reports any previous hypersensitivity to any of the components of Truvada;
• Has not used methamphetamine in the previous 72 hours and does not test positive for methamphetamine metabolites;
• Has not had unprotected anal intercourse with an HIV-positive or status unknown partner within the previous 3 months;
• Unwilling to comply with study requirements.

3 months