Effects of Substance Use on Condomless Anal Sex in a Large Sample of Adolescent Men Who Have Sex with Men: A Within and Between Relationship Design.

Substance use is a significant risk factor for HIV infection among adolescent men who have sex with men (AMSM). Substance use may reduce the use of HIV prevention measures or increase the likelihood of engaging in activities with a higher risk of HIV transmission, but there is a lack of studies dedicated to analyzing these mechanisms in adolescents and young MSM. This study aimed to explore the impact of substance use on condomless anal sex (CAS) in a large, racially diverse sample of AMSM. Additionally, we investigated how an individual's general level of substance use moderated the association between substance use before sex and CAS at the partnership level. Baseline data for an HIV prevention intervention were collected through online surveys from April 2018 to June 2020. The sample consisted of 1624 AMSM (M age, 16.69 years) who reported at least one sexual partner in the previous 3 months. Participants provided information about their three most recent sexual partners, including their relationship to the partner, PrEP use, frequency of alcohol, marijuana, and non-prescription drug use before sex, and the number of CAS acts. Participants also completed measures of their substance use frequency. Multilevel modeling in Mplus was used for data analysis, accounting for sexual partnerships nested within participants. All models controlled for PrEP use and relationship status. Results revealed a significant positive association between the frequency of non-prescription drug use before sex and CAS at the partnership level. This indicates that higher non-prescription drug use frequency before sex was associated with a greater number of CAS acts with partners. Moreover, the cross-level interaction between alcohol frequency and non-prescription drug use before sex was statistically significant. Specifically, for participants with high alcohol frequency scores, there was a significant positive association between non-prescription drug use before sex and CAS at the partnership level. AMSM with higher average alcohol consumption were more likely to engage in CAS when using non-prescription drugs prior to sex with a partner, compared to those with lower alcohol consumption. This study's use of multilevel data analysis contributes innovatively to the field by shedding light on how substance use operates within sexual relationships and different partnership dynamics. Tailored interventions targeting substance use should be developed to reduce HIV risk among AMSM.