Fentanyl, xylazine, and bromazolam: Urine toxicology trends in a San Francisco safety net opioid treatment patient cohort 2023-2025.

OBJECTIVES

To gain insights on the illicit drug supply in San Francisco using urine toxicology of opioid use disorder intake patients to assess temporal trends and co-occurrence patterns and detect emerging compounds of concern. To inform local overdose prevention and opioid use disorder treatment efforts.

METHODS

We analyzed 1763 opioid treatment intake patient urine samples at a safety net clinic over 2.5 years from March 2023-August 2025. We assessed urine toxicology by untargeted liquid chromatography high resolution mass spectrometry (LC-HRMS) using an in-house library containing > 500 small molecules, including fentanyl analogs, nitazene compounds, non-FDA approved benzodiazepines, medetomidine, and xylazine. We calculated auto and cross correlations between pairs of drug classes to assess contemporaneous and lagged weekly associations between drug classes over the study period.

RESULTS

Xylazine was widely detected over the study period, with multiple spikes in prevalence. No nitazene compounds were ever detected. Fentanyl, methamphetamine, and cocaine were the most prevalent drug classes and fentanyl was correlated with both stimulants contemporaneously. Norcarfentanil was detected once, medetomidine was detected twice, and bromazolam was detected 23 times. Xylazine had an auto-correlation lag pattern suggestive of surges in prevalence lasting two weeks.

CONCLUSIONS

Urine toxicology of a relevant patient population establishes the presence of xylazine in the San Francisco drug supply. Multiple other compounds of concern for overdose risk were also intermittently detected. The highly dynamic prevalences of substances of concern for fatal overdose suggests the value of ongoing monitoring.