PROJECT SUMMARY In recent years, overdoses involving illicit cocaine, methamphetamine, and other stimulants, have increased nationally and in the overdose hotspot states of Massachusetts (MA) and Rhode Island (RI). Polysubstance use has long been a known risk factor for overdose. However, drug seizure data suggest that cocaine, methamphetamine, and counterfeit pills may be adulterated with fentanyl. The unintentional consumption of stimulants containing illicit fentanyl represents a major risk factor for opioid-driven overdoses, whereas the increasing availability and use of highly potent cocaine and methamphetamine in MA and RI pose a risk for stimulant-only overdoses. Understanding the drug use patterns and strategies used by people who use stimulants to prevent overdose is necessary to identify risk and protective factors for stimulant-involved overdoses. Mixed-methods research with individuals involved in drug distribution can also provide critical information into the mechanisms through which fentanyl and other adulterants may enter the stimulant supply. The testing of drug samples can further triangulate consumer and distributor perspectives regarding the potency and adulteration of the drug supply. Drug checking using Fourier-Transform Infrared (FTIR) spectroscopy enables the detection of all active adulterants in a sample, including fentanyl and its analogs. When paired with confirmatory testing, drug checking can provide insights into the changing drug supply, the risk of exposure to highly potent or fentanyl-adulterated stimulants and overdose risk for high-risk communities. Finally, collaborative efforts with community stakeholders are needed to identify optimal, feasible, and acceptable strategies to prevent fatal and non-fatal overdoses in high-risk communities. Our overall objective is to reduce stimulant-involved overdoses in regions disproportionately affected by the overdose epidemic. Our approach to meeting this long- term objective is to utilize a multi-pronged approach to identify risk and protective factors for stimulant-involved overdose and use these findings to begin the process of developing a package of locally-tailored intervention strategies that can be swiftly implemented in future research to prevent stimulant-involved overdoses. Consistent with Objective 2 of RFA-CE-21-002, we aim to [1] Carry out mixed-methods research with people who use or distribute illicit stimulants to identify risk and protective factors for stimulant-involved overdoses; [2] Conduct drug checking to examine the potency of stimulants and the presence and relative quantity of fentanyl and other adulterants in the stimulant supply; and [3] Convene a series of working groups with individuals involved in primary and secondary overdose prevention in MA and RI to contextualize our mixed-methods findings and identify multilevel intervention strategies to prevent stimulant-involved overdoses. Completion of this study will yield a rich understanding of the social epidemiology of stimulant-involved overdoses in two states disproportionately affected by the overdose crisis. Findings will yield community-derived intervention strategies that can be readily implemented and scaled to prevent stimulant-involved overdoses in MA, RI, and beyond.