Xylazine is being replaced at least in part by a dangerous new sedative, medetomidine, in the drug supply.

The details:

• Medetomidine is in the same family as xylazine and clonidine (alpha-2 agonist).
• Like xylazine, medetomidine is sometimes used in veterinary settings, but it is also used for sedation in humans.

The context: As law enforcement officials have cracked down on xylazine, a form of medetomidine known as dexmedetomidine or “dex” has rapidly taken its place.

• Cracking down on xylazine created market pressure for a replacement with similar properties. But cracking down on medetomidine could jeopardize access to a commonly used medication.

The data:

• In the past year, medetomidine has become increasingly common in the drug supply, with cities including Philadelphia, Pittsburgh, Chicago, and San Francisco reporting cases of medetomidine-involved overdoses.
• In Philadelphia in particular, reports have skyrocketed. When the city first started testing for the substance in May 2024, it found medetomidine in 29% of fentanyl samples analyzed. Six months later, medetomidine’s prevalence increased three-fold to 87%, while xylazine’s dropped from nearly 100% early in the year to 42% in November.

Why it’s important: Medetomidine is causing severe health complications among people who use drugs.

• Overdose symptoms include low heart rate and strong sedation. Patients often do not respond to naloxone.
• Withdrawal symptoms include elevated heart rate and blood pressure that can damage organs including the heart and brain, symptoms that are worse than those associated with xylazine withdrawal.
• But: Unlike xylazine, medetomidine has not been known to cause wounds.

What’s coming: Public health, medicine, and harm reduction officials are beginning to respond to medetomidine, learning how to treat withdrawal, issuing warnings, and creating test strips.