['Although evidence suggests that antiretroviral (ARV) regimens containing nonnucleoside reverse transcriptase inhibitors (NNRTIs) are superior to single-protease inhibitor (PI)-based regimens at suppressing viral load, it is unclear how much of the improved viral suppression is due to intrinsic drug potency versus higher levels of adherence to simpler regimens. We therefore examined adherence and viral suppression in NNRTI and single-PI regimens in a cohort of largely ARV-experienced participants by using objective measures of adherence.', "Participants were recruited from the Research on Access to Care in the Homeless (REACH) Cohort and were included in the study if they were on single-PI-based or NNRTI-based highly active antiretroviral therapy (HAART) regimens for at least 3 months prior to study entry. Adherence was measured by unannounced pill counts at the participant's usual place of residence. The primary outcome was suppression of HIV viral RNA to <50 copies/mL.", 'Among 109 individuals who were followed for a median of 8.7 months, the odds of virologic suppression were approximately 8 times higher (p < .01) for participants on NNRTI-based regimens (n = 53) compared with those using single-PI-based regimens (n = 56) when controlling for adherence, as well as other potential confounders in a multivariable analysis. The only other independent predictors of viral suppression in multivariable modeling were ARV adherence (p < .01), CD4 nadir (p = .02), and continuous months on current regimen prior to the start of adherence monitoring (p < .01). There was no significant difference in adherence by unannounced pill counts in participants receiving NNRTI- versus single-PI-containing regimens.'] Are higher rates of viral suppression with nonnucleoside reverse transcriptase inhibitors compared to single protease inhibitors explained by better adherence?