High variation in purity of consumer-level illicit fentanyl samples in Los Angeles, September 2023-April 2025

The illicit manufacture of fentanyl results in product of unknown purity, contributing to overdose risk. However, data on the purity of illicitly manufactured fentanyl (IMF) in the United States typically comes from law enforcement sources and almost no information relevant to retail-level product is made available. We aim to quantify IMF purity among samples from a community-based drug checking program operating at four geographic sites in Los Angeles, California.

Drug samples (n = 1763) were obtained from participants who also answered an anonymous survey about sample characteristics. Qualitative and quantitative analysis were conducted leveraging directly observed mass spectrometry (DART-MS) and liquid chromatography mass spectrometry (LC/MS) respectively. LC/MS quantified a panel of compounds including fentanyl and fluorofentanyl. Composite IMF purity was estimated by adding the percent mass of fentanyl and fluorofentanyl.

A total of 353 samples had either fentanyl, fluorofentanyl, or both quantified between September 2023 and April 2025. Median IMF purity was 5.8 %, mean 10.0 %, SD 11.1 %, range 0.1-64.9 %. Samples expected to be fentanyl (n = 308) had higher median purity (7.0 %) compared to those expected to be heroin (n = 24, median purity 1.4 %) or other drugs (p < 0.001). Powder samples (n = 318) had higher median concentration (6.9 %) compared to pills (n = 11, 0.7 %) or tar (n = 22, 1.4 %) [p < 0.001]. Of expected-fentanyl samples, 42.5 % (n = 131) had an IMF purity of <5 %, while 17.5 % (n = 54) had purity over 20 %.

We found high variation in IMF purity among samples sold as fentanyl, even among samples obtained on the same day, in the same location. This volatility likely plays a role in high overdose risk, even among people with opioid tolerance, in the fentanyl era. Further research is needed to compare these findings to other locations across the United States.