Prevalence of fentanyl in methamphetamine and cocaine samples collected by community-based drug checking services.

Background: Overdose deaths involving stimulants and opioids simultaneously have raised the specter of widespread contamination of the stimulant supply with fentanyl.

Methods: We quantified prevalence of fentanyl in street methamphetamine and cocaine, stratified by crystalline texture, analyzing samples sent voluntarily to a public mail-in drug checking service (May 2021-June 2023). Samples from 77 harm reduction programs and clinics originated in 25 US states.