What are nitazenes and xylazine, and why are they in the news?
One is an opioid invented in the 1950s that never became a medicine; the other is an animal sedative that is not an opioid at all. Both now turn up in the illegal drug supply.
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Which one is it?
Nitazenes and xylazine are two substances that public health agencies have warned about in the past few years, and they are quite different from each other.
Nitazenes are opioids. They were developed in the second half of the 1950s by the Swiss company Ciba AG as pain-relieving agents, but they were never included in any and have not been approved for human use. Pharmacology references describe a few nitazenes as matching fentanyl's high potency in humans, and some as exceeding it. They came back into view in 2019, when isotonitazene was first identified in illicit drug samples and implicated in overdose deaths in Europe, Canada and the United States. Nitazenes have also been found in pills missold as other drugs, such as benzodiazepines. The British government reported more than 400 overdose deaths from nitazenes in the 18 months through January 2025.
Xylazine is not an opioid at all. It is a common veterinary drug used for sedation and pain relief in animals such as horses and cattle, and it acts on a different receptor, the alpha-2 adrenergic receptor. Bayer discovered it in 1962 as a blood-pressure drug, but human trials found that it depressed the , so it was marketed instead as a veterinary . In April 2023 the US government declared xylazine-laced fentanyl an emerging drug threat, and in 2022 the DEA reported xylazine in 23% of seized fentanyl powder and 7% of fentanyl pills.
Nitazenes
- A class of opioids from the 1950s
- Never approved for human use
- Some match or exceed fentanyl in potency
Xylazine
- Not an opioid
- A veterinary since the late 1960s
- Found in seized fentanyl powder and pills
The common thread is that both appear in the illegal supply, where nobody can see what a pill contains. As of 2022, recreational xylazine was almost always combined with opioids, and the treatment of a xylazine overdose primarily involves maintaining breathing and blood pressure.
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Recap
A new opioid and a non-opioid sedative are two ways an illegal supply can change; neither was ever approved for people.
💡 A trick to remember it · One was a drug that never made it out of the lab, the other a barn sedative that made it into pills.
Surprising fact · Xylazine began as a human blood-pressure drug in 1962 before becoming a veterinary sedative.
Connects to
- 🚢 How does illicit fentanyl reach the US, and what are precursor chemicals?
- 🧯 How does naloxone reverse an opioid overdose, and why can it wear off before the opioid does?
- 🫁 Why does an opioid overdose stop your breathing?
- ⚗️ Why is fentanyl so potent that tiny amounts can kill?
- 😴 Why did surgeons race against the clock until a dentist put a patient to sleep in 1846?
Sources (4)
No source, no claim. Every fact in this lesson (15 claims) cites at least one of these.