Scheduling Xylazine Didn’t Make It Disappear. It Made Room for Something Worse.

In Philadelphia, between May 2024 and March 2026, the share of street dope samples testing positive for xylazine fell from 97% to 28%. In that same window, a veterinary sedative almost nobody outside a vet clinic had heard of two years ago went from showing up in 29% of samples to 90% of them, according to CDC surveillance data. That drug is medetomidine, and it didn’t wander into the supply by accident. A study published August 7 in the International Journal of Drug Policy and reported by Healio gives the clearest evidence yet that it moved in because xylazine got scheduled.

Scheduling a drug doesn’t clear it out of the supply. It clears shelf space for whatever replaces it.

Researchers David T. Zhu and Sehun Oh pulled data from the federal database of what crime labs actually find when they test seized drug samples, not what people report using — NFLIS, formally the National Forensic Laboratory Information System — going back to 1999, across 14 states. They tracked what happened after each state formally scheduled xylazine as a controlled substance, the “tranq” cutting agent that’s been showing up in fentanyl since the early 2020s and causing the wounds you’ve probably heard about, the ones that don’t heal and don’t respond to naloxone. The finding: after scheduling, medetomidine detections rose sharply. Xylazine detections did not correspondingly fall. Out of 101,987 xylazine reports and 12,085 medetomidine reports across those states, scheduling was tied to roughly 1,536 additional medetomidine detections per 100,000 drug samples. The researchers are confident that number is real and not a fluke — statisticians express that confidence as a range, called a 95% confidence interval (211.1–2861.9 here), meaning the true effect almost certainly falls somewhere in that span rather than at zero.

Zhu and Oh frame this as another instance of a pattern drug policy researchers have a name for: crack down on one substance and the market doesn’t shrink, it adapts — usually toward something more concentrated, more potent, or harder to detect, because that’s what survives a ban. Researchers call it the iron law of prohibition. It’s the same mechanism that turned fentanyl into the dominant opioid once heroin supply chains got squeezed, and the same one that pushed nitazenes — a class of synthetic opioids stronger than fentanyl — into the supply once fentanyl analogs themselves got scheduled. Medetomidine is the latest substitute, and by most measures a worse one.

The Supply Already Ran This Experiment Without Waiting for the Study

You don’t need a confidence interval to see the substitution happening — the CDC Health Alert Network has been watching it unfold nationally since it issued an advisory on April 2. Medetomidine reports to NFLIS went from 247 in 2023 to 2,616 in 2024 to 8,233 in 2025 — a rise of more than 950% in two years. Medetomidine is a veterinary sedative, related to the animal tranquilizer dexmedetomidine, and CDC estimates it’s up to 300 times more potent than xylazine. It drops heart rate hard — cases have shown pulses as low as 32 beats per minute — and it produces a withdrawal syndrome that doesn’t look like opioid withdrawal and doesn’t respond to standard naloxone protocols, because it isn’t an opioid. Nearly all of it, 98% of medetomidine-positive samples tested between July and December 2025, also contained fentanyl, meaning it’s not replacing your opioid, it’s riding shotgun with it, changing what an overdose looks like and what reverses it.

The Tool That Would Let You Know Is the One Getting Cut

If you use, or you’re the person a friend who uses calls first, a test strip is one of the only ways to find out what’s actually in a bag before it’s in you — not perfect, not a guarantee, but real information you can act on. That’s precisely the tool getting harder to get. STAT News reported that on April 24, SAMHSA told federal grantees they can no longer use federal money to publicly distribute fentanyl test strips, xylazine or medetomidine test strips, sterile syringes, pipes, or overdose hotlines. Naloxone funding was preserved — that’s the one piece of harm reduction infrastructure still standing, and it’s worth knowing where the nearest kit is tonight, because it still works on the opioid part of what’s out there even when it can’t touch the sedative.

But naloxone alone doesn’t tell you what you’re using, and it doesn’t reverse medetomidine’s crashing heart rate or its withdrawal. Test strips are the tool that turns “I think this might have tranq in it” into something closer to knowing. Cutting funding for the exact strips that would flag a substitute the government’s own scheduling policy helped create isn’t a coincidence of timing — it’s two federal decisions moving in opposite directions on the same drug.

Test strips are the tool that turns “I think this might have tranq in it” into something closer to knowing.

Zhu and Oh aren’t arguing xylazine should go unregulated. They’re arguing that scheduling without also funding surveillance and drug-checking is a policy that manages optics, not overdose risk. The supply doesn’t read legislative text. It just moves toward whatever’s still working — and right now, the thing tracking where it moves is losing its funding faster than the thing it’s tracking is losing users.