Velloza J, Bacchetti P, Hendrix CW, et al. - As adherence determines the effectiveness of oral emtricitabine (FTC)/tenofovir (TFV) disoproxil fumarate–based HIV preexposure prophylaxis (PrEP), researchers sought for pharmacologic measures that may assist in interpreting patterns and predictors of PrEP adherence. From the subsample of men who have sex with men enrolled in HPTN 067/ADAPT in Bangkok, Thailand, and Harlem, NY, U.S, data were analyzed. After a 5-week directly observed therapy period, they randomized 350 participants (median age: 31 years, interquartile range: 25–38) to daily, time-driven, or event-driven PrEP. Short- and long-term PrEP use was shown by plasma and hair FTC/TFV levels, respectively. In multivariable models, lower hair FTC/TFV concentrations were observed in correlation with being enrolled in Harlem, being in non–daily arms, and having less than college education; higher concentrations were observed in correlation with heavy alcohol use. For plasma concentrations by site and arm, they gained similar results, but higher concentrations were noted in correlation with older age and greater number of sex partners. They observed correlation between plasma, hair, and Wisepill data in HPTN067, and hence these could serve as complementary adherence measures.