Inclusion Criteria:  Assigned male at birth Identifies as male Age 18 or older Reads and speaks English Past 6 months, reports condomless anal sex (CAS) with men HIV negative Currently has an active prescription for daily oral PrEP and reports any non-adherence in the past month Has an iPhone or Android smartphone Screens positive for a moderate or severe stimulant use disorder with an abbreviated version of the Alcohol, Smoking, and Substance Involvement Screening Test (ASSIST) Lives within catchment area (South Florida, San Francisco Bay area)  Exclusion Criteria:  Unable to provide informed consent Unwilling to participate in smartphone-based CM for directly observed PrEP doses Unwilling to provide dried blood spot (DBS) specimen Plans to move out of the state in the next 6 months Not taking PrEP daily (e.g., if taking intermittent 2-1-1 dosing) Switched from Truvada to Descovy in the last 5 months