“…People who use drugs (PWUD) rely on an unregulated, ever-changing illicit market, resulting in uncertainty of what they are using ( Bhuiyan et al, 2023 ). The desired substance, if present, is often only a fraction of the total, with filler or undesired substances comprising the rest ( Cruz et al, 2023 ; Żubryckaet al, 2022 ). Without knowing a substance's psychoactive components, PWUD are at increased risk for adverse health effects, including overdose.…”