Same name, different drugs: variability of fentanyl ('dope') products sold under the same label

Unregulated opioid markets are increasingly characterized by complex and variable drug compositions. In North-eastern and Mid-Atlantic US street opioid markets, fentanyl-containing powders are commonly sold in stamped glassine bags. These "stamps" function as branding and are often used by people who use drugs, harm reduction programs and public health agencies as informal indicators of product composition or risk. This study quantified the extent to which stamp identity is associated with the presence and concentration of fentanyl and co-occurring compounds.

We analyzed 1153 drug samples across 475 stamps collected during 2024-2025 in Philadelphia, Pennsylvania; Delaware; and Maryland. Laboratory testing identified compound presence and quantified concentrations. Multivariable logistic regression estimated stamp-specific probabilities of compound detection, and mixed-effects models generated intraclass correlation coefficients (ICCs) to assess clustering by stamp.

Fentanyl was nearly ubiquitous (95.3%) but varied widely in concentration within stamps (<1% to >20%), indicating that branding was a poor indicator of potency. Several adulterants, including medetomidine (prevalence: 64.8%) and xylazine (prevalence: 42.2%), exhibited moderate-to-high clustering by stamp (ICCs up to 0.70), but substantial within-stamp inconsistency remained. Predicted probabilities varied widely, with two-thirds of compound-stamp combinations between 20% and 80%. Concentration analyses demonstrated inconsistent dosing, particularly for fentanyl (ICC=0.15).

In this region, street opioid stamp branding is an unreliable indicator of fentanyl potency and only partially informative for some adulterants. Products sold under the same stamp often differ in composition and compound concentration, suggesting that stamp-based risk assessment is insufficient and reinforcing the value of sample-level drug checking.