Concomitant use of cocaine and HIV pre-exposure prophylaxis (PrEP) raises important clinical questions around adherence, retention in care, and renal toxicity. We assessed the associations of confirmed cocaine use with PrEP adherence (both ascertained through objective measures), care engagement, and renal function in the iPrEx open-label extension. Cocaine use was measured in scalp hair samples and categorized as light (500-3000 pg/mg) and moderate to heavy (>3000 pg/mg). PrEP adherence in the first 3 months was measured through plasma tenofovir concentrations. Disengagement from PrEP care was defined as a gap in follow-up greater than 4 months. Serum creatinine was assessed at baseline and quarterly visits. Of the 400 participants included in this analysis, 90% were men who have sex with men, 10% transgender women, 74% Hispanic/Latino; 21% tested positive for cocaine use in the last 3 months. In adjusted analysis, light cocaine use [adjusted odds ratio 2.10 (95% confidence interval: 1.07 to 4.14)] and moderate to heavy use [adjusted odds ratio 2.32 (1.08 to 5.00)] were associated with greater odds of having plasma tenofovir concentrations below the level of quantitation. Participants with moderate to heavy use had a nearly 3-fold higher rate of disengagement from PrEP care compared with nonusers (adjusted hazard ratio 2.90 [1.48 to 5.66]). We found no statistically or clinically significant differences in creatinine clearance and serum creatinine between participants who tested positive for cocaine and those who did not. Cocaine use decreases PrEP adherence and care engagement. Comprehensive approaches are needed to reduce cocaine use and enhance engagement along the PrEP care continuum.