MTN-003D was a VOICE protocol substudy, where a subset of former participants were asked to complete one or two additional visits after their participation in the trial had ended. If participants agreed to participate in the MTN-003D substudy, they completed an in-depth interview (IDI) and/or participated in a focus group discussion (FGD). MTN-003D investigated the factors influencing VOICE participants’ actual versus reported study product use and explored receptive anal intercourse (AI) behavior. In addition, motivations to join the trial, and risk perception in particular, were explored as one of the explanatory factors contributing to sub-optimal adherence. In Stage 2 of MTN-003D, participants were presented with their drug levels from blood samples collected during participation in VOICE. The drug levels were used as a tool to further explore product non-adherence and related behaviors. Primary results were presented at HIV Research for Prevention (HIV R4P) held on October 28-31, 2014 in Cape Town, South Africa. The two primary manuscripts were published in AIDS in October 2015 and AIDS and Behavior in August 2019 respectively.