NIST Study Maps How Fentanyl Adulterants Shift Across the U.S.

The illicit fentanyl sold in the United States is less and less a single drug and more a shifting cocktail of sedatives, industrial chemicals and other additives — and the mix is different depending on which side of the country a person is buying it. A National Institute of Standards and Technology study published October 7 in the journal Drug Testing and Analysis analyzed 4,563 samples of drug residue collected nationwide between January 2024 and June 2026 and found that the number of adulterants in a typical sample has climbed steadily, while the practice of cutting fentanyl varies sharply by region.

The research, led by NIST chemist Edward Sisco, is part of the agency's Rapid Drug Analysis and Research program, or RaDAR, which works with public health agencies, law enforcement, forensic labs and medical examiner offices to fingerprint street drugs within seconds.

What two and a half years of samples showed

In early 2024, a fentanyl sample usually carried one or two additives. By the end of the study period, six or more compounds in a single sample had become common, Sisco said.

"We are now tracking fentanyl additives over a wide geographic area, so we can see the movement of some of these additives over time," Sisco said, describing a path that runs "from Philadelphia, down to Delaware and Maryland, and then out west."

That tracking is possible because of a technique called Direct Analysis in Real Time Mass Spectrometry, which vaporizes a sample and produces a chemical fingerprint of everything in it. The RaDAR team used the method to identify trace compounds that conventional equipment can miss, then mapped where each adulterant appeared and when.

Xylazine fades, medetomidine moves in

The clearest regional split involves animal tranquilizers. Xylazine — the veterinary sedative that gave "tranq" its name — remains far more common in the eastern United States than in the West, where samples generally contain fewer additives but at higher concentrations.

The study also documents xylazine being displaced by medetomidine, a far more potent sedative that can produce severe withdrawal. Because neither drug is an opioid, naloxone does not reverse the sedation they cause, even when it restores breathing from the fentanyl itself. Wounds associated with xylazine can become severe enough to require amputation if they go untreated, NIST noted.

Treating those cases means more than overdose reversal; clinicians increasingly have to manage sedation, wounds and complicated withdrawal alongside opioid dependence.

An industrial chemical that keeps appearing

A newer additive in the data is BTMPS, an industrial chemical used in the manufacture of plastics. It has turned up in fentanyl samples in both the eastern and western United States since the summer of 2024, and NIST describes it as potentially toxic, capable of causing eye inflammation and a burning sensation.

The appearance of a non-opioid industrial compound in the drug supply is the kind of signal RaDAR was built to catch. "RaDAR enables NIST to immediately alert public health officials to the presence of new adulterants in their area, so that they can plan a more effective treatment for people who have consumed fentanyl," Sisco said.

Why the count of additives matters

Each additional compound makes a drug sample harder to read and an overdose harder to treat. Adulterants can deepen respiratory depression, prolong sedation, complicate withdrawal and complicate the medical picture for emergency departments that may be working from a patient's symptoms rather than a lab result.

"With more additives, it's both more difficult to analyze a sample and more difficult to treat a drug overdose," Sisco said. "Our goal is that if some new additive pops up, say in Philadelphia, we'll be able to tell public health officials when that additive is likely to show up in Delaware, Maryland or the West Coast."

Until that forecasting works, the study suggests the practical value of RaDAR is speed: telling a city what is actually in its local supply now, rather than months later when toxicology reports are complete.

A supply that keeps changing

The findings add granularity to a picture that federal agencies have been assembling piece by piece. The Drug Enforcement Administration flagged fentanyl mixtures containing medetomidine and other emerging compounds earlier this year, and state health departments from Utah to Louisiana have issued warnings after detections in local supplies.

What the NIST data adds is a consistent, national method for watching that supply move — and evidence that the trend line is toward more complexity, not less. For the people who use drugs and for the clinicians who treat them, the study argues that knowing the local recipe is becoming as important as knowing that fentanyl is present at all.