Drug checking results, participant characteristics, and service retention from a longitudinal community-based drug checking study in the United States

Background The volatile illicit drug supply continues to drive overdose and severe health harms among people who use drugs (PWUD). Community-based drug checking services (DCS) are a proactive harm reduction strategy; however, research on these services has relied on cross-sectional data, without examining participants’ engagement and drug samples over time. We conducted a quantitative panel drug checking study in the United States. Methods Between March and November 2025, 57 PWUD were recruited from a syringe services program providing DCS with Fourier-transform infrared spectroscopy (FTIR) in Minnesota. Participants completed a baseline survey and up to seven weekly follow-up surveys, each paired with a drug sample for testing. We assessed retention, compared participant expectations with drug checking results, and measured within-person drug source change as the proportion of person-periods in which participants reported that the submitted sample came from the same source as the prior week. Results Participants demonstrated sustained engagement, with 65% completing the final follow-up and intermittent re-engagement common among those who missed visits. Drug checking revealed substantial discordance between expected and detected substances. Fentanyl and methamphetamine were the most frequently detected drugs, yet recall, indicating participants’ ability to correctly identify substances relative to drug checking results, was moderate (65.8% and 45.9%, respectively). Xylazine was detected in nine samples, but no participants expected its presence. Frequency of drug source change was high, with participants indicating approximately four out of five weekly purchases came from a different source. Conclusions PWUD engage with community-based DCS when offered in harm reduction settings. Gaps between what participants believed they were consuming and what DCS detected—particularly, the complete lack of xylazine awareness—underscore the critical role of these services. While we show that longitudinal research with DCS embedded within syringe services programs is feasible, even among highly marginalized populations, we discuss strategies for improvement.