PROJECT SUMMARY/ABSTRACT DESCRIPTION: See instructions. This must contain a summary of the proposed activity suitable for dissemination to the public (no proprietary/confidential information). It should be a self-contained description of the project and contain a statement of objectives and methods to be employed. It should be informative to other persons working in the same or related fields. DO NOT EXCEED THE SPACE PROVIDED. We propose a mixed-methods study to investigate the positive and negative consequences of fentanyl test strip (FTS) use by people who inject drugs (PWID). Overdose (OD) deaths involving illicitly made fentanyl (IMF) increased 540% in the United States from 2013–2016 and another 45.2% from 2016–2017, with IMF- involved deaths outnumbering heroin and prescription opioid deaths for the first time in 2016. The rapid proliferation of IMF in the illicit drug market has led to a heightened risk environment characterized by adulterated products of unknown purity and potency. While naloxone is a proven secondary OD prevention strategy by preventing fatalities among OD victims, in the wake of the IMF flooding the drug markets, we now need primary OD prevention strategies to prevent ODs from occurring in the first place. Over the past 3 years, community-based organizations in the U.S. and Canada have started to distribute FTS as a primary OD prevention strategy. FTS are comparable to point-of-care pregnancy tests in that after a drug solution comes into contact with the test strip, the strip displays one or two red lines, denoting positive or negative results. FTS cost about $1, making them a reasonable cost to OD prevention programs. Little is known about the positive and negative consequences of PWID using FTS. This application proposes a rigorous prospective study of PWID, guided by Zinberg’s Drug, Set, and Setting model. The specific aims are as follows: Aim 1: To assess positive behavioral health consequences associated with FTS use in a cohort of PWID in North Carolina (N=350) and West Virginia (N=350). Aim 2: To assess negative behavioral health consequences associated with FTS use in a cohort of PWID in North Carolina and West Virginia. Aim 3: To conduct qualitative interviews with PWID (n=100) to learn how Drug, Set, and Setting factors influence the use of FTS, drug purchasing and drug use behavior, and OD risk. To achieve these aims, we will recruit a sample of 700 PWID from two syringe service program sites: Greensboro, NC, and Morgantown, WV. West Virginia had the highest fentanyl OD death rate in the U.S. in 2017, and North Carolina had the second highest rate increase (2016–2017) in fentanyl OD deaths. For Aims 1 and 2, we will collect quantitative data pertaining to FTS use and drug, set, and setting factors at baseline, 6 months, and 12 months. For Aim 3, we will purposively sample a subset of 100 PWID from the quantitative cohort. The study is led by Multiple Principal Investigators, Jon Zibbell, a National Institute...