What Is in Street Fentanyl Now: A New Federal Study Found Six or More Additives Per Sample

Last week, the National Institute of Standards and Technology, the federal lab better known for measuring things precisely, published a study on what is actually in street fentanyl.

The answer is: more than ever.

NIST chemists analyzed 4,563 samples of drug residue collected across the country between January 2024 and June 2026. The study was published October 7 in the journal Drug Testing and Analysis. Here is what they found.

• In early 2024, a typical sample contained one or two additives. Now six or more is more common.
• Animal tranquilizers like xylazine are much more common on the East Coast than in the West.
• Xylazine is being replaced by medetomidine, a much more potent sedative that can cause severe withdrawal.
• An industrial chemical called BTMPS, used in making plastics, has been showing up in fentanyl in both the East and the West since the summer of 2024. NIST says it can cause eye inflammation and burning.
• Additives rise and fall in cycles, and they move. The lead researcher, Edward Sisco, described tracking them from Philadelphia to Delaware and Maryland, and then out west.

Sisco said more additives make a sample harder to analyze and make an overdose harder to treat.

That last part is why I am writing this.

Why the additives matter

Most of these additives are not opioids. That matters because naloxone, the overdose reversal drug sold as Narcan, only reverses opioids.

NIST put it plainly: most of the harmful compounds are not opioids, so they need additional medical treatment beyond naloxone.

The FDA warned about this back in 2022, when it told doctors that naloxone may not be able to reverse the effects of xylazine mixed into fentanyl.

So here is the situation a family can walk into. Someone overdoses. You give Narcan. Their breathing comes back, but they will not wake up. That does not mean the Narcan failed. It may mean the fentanyl was reversed and a sedative is still on board.

Medetomidine: the one to know about

Medetomidine is a veterinary sedative approved for dogs. It is not approved for people. On the street it goes by names like rhino tranq, mede or dex.

In April, the CDC and the White House drug policy office issued a national health advisory about it. The numbers in that advisory are hard to ignore. Federal forensic labs logged 247 reports of medetomidine in drug seizures in 2023, then 2,616 in 2024, then 8,233 in 2025.

In 2025, most of those reports came from the Northeast (52%) and the Midwest (31%). The South, which includes Arkansas, accounted for 17%. The West was under 1%. The CDC said its spread appears to be expanding.

Of the drug samples that tested positive for medetomidine in the second half of 2025, 98% also contained fentanyl. People buying fentanyl are getting medetomidine whether they know it or not.

I have not seen public data showing medetomidine in Arkansas specifically, and I am not going to claim it is here. What I can tell you is that things that start in Philadelphia have a way of showing up in Arkansas later. The Arkansas Department of Health warned in 2023 that the Arkansas State Crime Laboratory had found xylazine mixed into fentanyl and heroin here. I wrote last month about cychlorphine, a new opioid found in Arkansas. The supply here changes too.

The withdrawal problem

This is the part that worries me most as a doctor who treats opioid addiction.

The CDC says stopping medetomidine after regular use can cause a severe withdrawal, similar to clonidine withdrawal, that can require emergency or intensive care. The signs it lists are:

• A racing heart, over 100 beats a minute
• Very high blood pressure
• Going in and out of alertness
• Shaking
• Chest pain
• Vomiting that will not stop

The CDC says these symptoms can start within hours of last use and peak 18 to 36 hours later. Complications reported with severe cases include heart damage and a dangerous brain swelling condition.

That is not the withdrawal most families are used to seeing.

The CDC's advice to people at risk: go to the hospital or call 911 if you cannot stop throwing up, have chest pain, are going in and out of awareness, or are having severe withdrawal symptoms.

So if someone you love has been using street fentanyl and tells you they are going to quit cold turkey at home this weekend, please hear me. That plan was risky before. With today's supply, it can be dangerous. The safer path is to get medical help to stop.

What this means for starting treatment

When I start someone on buprenorphine, the medication in Suboxone, I need to know what they have been using. Fentanyl already makes the start more complicated. I explain why in starting Suboxone after fentanyl.

With more additives in the supply, the honest answer to "what have you been using" is often "I don't really know." That is fine. Tell me that. Tell me what it looked like, what it was called, how it made you feel, and whether withdrawal has felt different lately. If it sounds like something more than opioid withdrawal, I will send you to the emergency room first. That is not me turning you away. That is me keeping you safe so we can start treatment after.

The CDC's own advisory ends where I would: addiction is a treatable chronic condition, and there are effective treatments, including medications for opioid addiction.

The additives are a moving target. Getting off the street supply is not.

What to do if someone overdoses

These steps come from the CDC and NIDA. They apply whether or not you think a sedative is involved.

1. Call 911.
2. Give naloxone. Experts recommend giving it even if you suspect xylazine or medetomidine, because fentanyl is almost always present too.
3. If they are not breathing, give rescue breaths. The CDC says to tilt the head back, pinch the nose, give two slow breaths, then one breath every 5 seconds.
4. The CDC says naloxone can be repeated every 2 to 3 minutes as needed so the person takes at least one breath every 5 seconds.
5. The goal is breathing, not waking up. CDC guidance says to give the naloxone needed to restore breathing rather than trying to restore alertness.
6. Put them on their side with the airway clear.
7. Stay with them until help arrives.

If you have questions afterward, the Arkansas Poison Center is at 1-800-222-1222.

Wounds are a warning sign

Xylazine causes skin wounds that can get infected quickly. The CDC says that when caught early, they can be managed with basic wound care, but left untreated they can lead to amputation or become life-threatening.

If someone you love has sores that will not heal, especially on the arms or legs, that is a reason to get them to a doctor now, and a sign that what they are using contains more than fentanyl.

How I can help

I was an orthopedic surgeon. I lost that career to addiction, and I recovered. I treat adults with opioid use disorder at 102 E Sunbridge Dr, Suite 3, in Fayetteville.

I answer my own phone 24 hours a day, every day of the year, at 479-856-1505. I will come in at any hour if you need to be seen.

A scheduled visit is $200. An unscheduled after-hours visit is $300. Follow-ups are about every 28 days. I do not bill insurance, but insurance can still be used at the pharmacy for the medication and for lab work.

Your records are protected under HIPAA and 42 CFR Part 2, the federal rule that gives addiction treatment records extra privacy.

If you are thinking about detox instead, read medical detox vs. Suboxone treatment first.

You do not need to know what was in it. You just need to call.

More reading: What the first visit looks like · What treatment costs