Project Summary We propose a one-year, Administrative Supplement to our parent grant (R01DA05672) to qualitatively examine the use homelessness relationship between experiences of community supervision (i.e., probation and parole) and polysubstance patterns, overdose vulnerability, and substance use t reatment in a sample of people experiencing with fentanyl-stimulant polysubstance use. People experiencing homelessness who use drugs are disproportionately engaged the criminal legal system and those who are racially minoritized are most impacted by the negative consequences of this engagement (e.g., arrest and incarceration). In 2020, approximately 4 million people in the US were on community supervision, which includes limitations on freedom of movement, time, and social contacts, as well as mandatory urine toxicology screening during the period of probation and parole. Formerly incarcerated people experience higher rates of homelessness, but the role that community supervision plays in shaping access to housing post-release is not well understood. Overdose vulnerability increases in the period immediately following release from jail and/or prison, due to decreased tolerance, changes to the drug supply, and atrophied social networks. However, little is known about the relationship between community supervision and overdose vulnerability, especially for people experiencing homelessness who co-use stimulants and fentanyl. In addition, the relationships between fentanyl-stimulant polysubstance use, community supervision, and access to substance use disorder treatment has yet to be studied. Extending the scope of the parent grant and building on our extensive experience studying drug use, homelessness, and community supervision, we propose the following specific aims: CLS.SA1: To characterize how community supervision shapes fentanyl-stimulant polysubstance use among people experiencing homelessness, including polysubstance use patterns and drug use practices. CLS.SA2: To explore how community supervision impacts overdose disorder vulnerability, access to housing, and substance use treatment among people experiencing homelessness with fentanyl-stimulant polysubstance use. Informed by the equity-focused Intersectional Risk Environment framework, we will conduct qualitative interviews with enrolled parent study participants who are on community supervision in San Francisco (n=25), and analytically compare those experiences to parent study participants not engaged in community supervision. Data garnered from this administrative supplement will generate emergent lines of inquiry for future R01 proposals and be used to offer recommendations for this population that are scalable and adaptable to other US cities through the parent study's extensive community stakeholder engagement processes. This study is aligned with priorities of the current Notice of Special Interest (NOT-OD-23-011) by examining the relationship between criminal legal system involvement,...