State xylazine scheduling and changes in xylazine and medetomidine reports in the U.S. illicit drug supply: A quasi-experimental study.

BACKGROUND

Xylazine and medetomidine are veterinary sedatives increasingly detected as adulterants in the U.S. illicit drug supply. In response, several states have scheduled xylazine; none have scheduled medetomidine during the study period. Whether xylazine scheduling was associated with subsequent changes in xylazine and medetomidine detections remains unclear.

METHODS

We conducted a state-level, semiannual, serial cross-sectional study using National Forensic Laboratory Information System (NFLIS) data on drug samples from 1999 to 2025. The primary outcomes were xylazine and medetomidine reports per 100,000 NFLIS drug reports. We used staggered difference-in-differences event-study models to estimate changes in report rates after xylazine scheduling. Sensitivity analyses excluded Florida and expanded the treatment definition to include states that criminalized xylazine without formal scheduling. Falsification analyses examined steroid and antidepressant reports as negative-control outcomes.

RESULTS

NFLIS recorded 101,987 xylazine reports and 12,085 medetomidine reports. Xylazine scheduling was not associated with a significant change in xylazine report rates (ATT, 2872.3 per 100,000; 95% CI, -2024.6 to 7769.2; p=.250). In contrast, xylazine scheduling was associated with a significant increase in medetomidine report rates (ATT, 1536.5 per 100,000; 95% CI, 211.1 to 2861.9; p=.023). Sensitivity analyses produced similar findings. Negative-control outcomes showed no significant changes.

CONCLUSIONS

State xylazine scheduling was associated with increases in medetomidine reports but no significant change in xylazine reports. These findings suggest that scheduling may be followed by changes in adulterant composition rather than reductions in overall α2-adrenergic agonist involvement. Our study highlights the importance of monitoring the unintended effects of xylazine scheduling and supporting continued investment in public health surveillance, drug checking, and harm reduction services.