Fentanyl Adulterants: What New NIST Research Reveals

A new NIST study of fentanyl adulterants has documented how quickly the chemical composition of illicit drugs can change. Using thousands of drug-checking results collected between January 2024 and June 2026, researchers found substantial differences across U.S. regions, a shift from xylazine toward medetomidine in some markets, and increasingly complex mixtures. For forensic toxicologists, the findings are a reminder that a method designed to detect yesterday’s drug supply may miss tomorrow’s emerging compounds.

The research, led by Edward Sisco at the U.S. National Institute of Standards and Technology (NIST), was published online in Drug Testing and Analysis on October 7, 2026. NIST announced the findings on October 8. The study is part of the agency’s Rapid Drug Analysis and Research (RaDAR) program, which works with public-health, law-enforcement and forensic partners to provide timely information about the changing drug supply.

What did the NIST fentanyl adulterants study examine?

The paper, Trends in Fentanyl Adulteration From Rapid Drug Analysis and Research (RaDAR) Drug Checking Samples, January 2024 to June 2026, assessed 4,563 qualitative results and 1,224 quantitative results from samples collected across 17 U.S. states. These are drug-product and residue dataInformation in analog or digital form that can be transmitted or processed. Read Full Definition, not blood or other biological toxicology specimens. Qualitative testing addresses which substances are present; quantitative testing estimates how much of a substance is present in the analyzed material.

This distinction matters. Detection of a chemical in a seized or submitted drug sample does not establish that a particular person consumed it, nor does it independently establish a cause of deathThe cause of death refers to the specific injury, disease, or underlying condition that directly leads to an individual's demise. It is a critical determination made by medical professionals, such as Medical Examiners or Coroners, Read Full Definition. Those questions require case-specific evidenceEvidence is any form of proof, such as objects, materials, or scientific findings, presented to establish or disprove a fact in a legal proceeding. It is used to reconstruct events and link or exclude individuals Read Full Definition, appropriate biological testing and interpretation.

Five findings that forensic laboratories should know

1. Xylazine and medetomidine are changing places in some markets

Xylazine, a veterinary sedative that has appeared in illicit fentanyl, was more prevalent in eastern than western U.S. samples. NIST observed a shift toward medetomidine, another nonopioid sedative, in parts of the supply. The change was not uniform across the country: local trends and timing differed.

Medetomidine is particularly important because it can produce pronounced sedation and severe withdrawal. The CDC’s April 2026 situation summary notes that exposure may be followed by dangerous withdrawal symptoms that require emergency medical care. For toxicology laboratories, a suspected opioid case with unexpectedly prolonged sedation or unusual withdrawal findings may warrant consideration of drugs outside a routine opioid panel.

2. The composition of fentanyl samples is becoming more complex

NIST reported that samples commonly containing one or two additional compounds in early 2024 increasingly gave way to mixtures containing six or more compounds. Local anesthetics, veterinary sedatives and industrial chemicals may be present alongside illicitly manufactured fentanyl. Compounds can rise and fall in prevalence independently, making a fixed list of presumed adulterants increasingly unreliable.

The practical problem is not simply the number of peaks in a spectrum. Complex mixtures can create additional analytical and interpretation challenges, particularly when multiple components are present at widely different levels or when laboratories lack suitable reference standards.

3. BTMPS has appeared in both eastern and western samples

Among the substances identified was BTMPS, short for bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, an industrial chemical used in plastics manufacturing. NIST reported its detection in fentanyl samples in both regions beginning in summer 2024. Its presence illustrates why forensic drug testing cannot focus exclusively on controlled narcotics or familiar cutting agents. The toxicological consequences of exposure to unusual additives may also be incompletely characterized.

4. Eastern and western samples showed different patterns

The study found that western samples generally contained fewer additional compounds, while the concentrations of some detected components were higher. In the quantitative subset, the authors reported approximate average fentanyl mass fractions of 13% in western samples and 5% in eastern samples. These percentages describe the sampled material, not all illicit fentanyl circulating in either region.

Forensic scientists should resist treating regional averages as expected concentrations for an individual exhibit. Individual samples can differ substantially, and the particular RaDAR sampling network does not constitute a random census of the national illicit drug supply.

5. Fast chemical intelligence can support earlier alerts

One of RaDAR’s strengths is speed. An emerging substance detected in one location can be communicated to partner laboratories and health agencies before traditional, slower reporting systems have assembled a broader picture. NIST researchers are exploring how geographic trends might help anticipate where an adulterant could appear next. That is a surveillance objective, not a proven ability to predict the composition of an individual sample.

How DART-MS helps detect emerging drug adulterants

NIST uses Direct Analysis in Real Time Mass Spectrometry (DART-MS) as a rapid screening technique. A sample is ionized at atmospheric pressure, and the mass spectrometer detects ions that help analysts recognize compounds by their mass-spectral signatures. This approach can produce useful screening information in seconds without the chromatographic separation required by many conventional workflows.

Speed, however, should not be confused with a fully confirmed quantitative result. Depending on the compoundIn scientific terminology, a "compound" refers to a substance formed by the combination of two or more different elements or molecules. These elements or molecules can be chemically bonded together to create a new substance Read Full Definition and sample matrix, mixtures can present challenges such as overlapping signals, ionAn ion is a type of chemical species that results from the unequal number of electrons and protons in an atom or molecule. This imbalance in charge gives ions an electric charge, either positive or Read Full Definition suppression and structural isomers. Laboratory methods must be validated for their intended purpose. NIST explains that its RaDAR workflow uses additional chromatography-based mass spectrometry for selected confirmation and quantification, including investigation of newly detected substances.

For readers who want background on separation and measurement techniques, see Simply Forensic’s guide to forensic chromatography and its applications and its discussion of benchtop NMR as a method for quantifying illicit drugs. These methods serve different purposes, and none should be treated as interchangeable without validationValidation, often referred to as method validation, is a crucial process in the laboratory when introducing a new machine, technology, or analytical technique. It involves a series of systematic steps and assessments to ensure that Read Full Definition.

What does the study mean for forensic toxicology casework?

The immediate value lies in method review and intelligence sharing rather than in replacing established evidential testing. For laboratories handling seized drugs, postmortem samples or clinical specimens, the following priorities deserve attention:

• Review target analytes: Check whether screening and confirmation panels include locally relevant emerging sedatives and adulterants, and review them as prevalence changes.
• Separate screening from identification: Document the evidential status and limitations of rapid screening results; perform appropriate confirmatory testing where required.
• Maintain suitable reference materials and validation: Evaluate detection limits, selectivity, matrix effects, compound stability and analytical interference before expanding casework scope.
• Share emerging-drug information: Use verified alerts from accredited laboratories, medical examiners and public-health agencies to prioritize method development.
• Interpret biological findings cautiously: Finding a drug in a product does not establish exposure, impairment or causation in a person. Postmortem interpretation, in particular, requires clinical and case circumstances.

The public-health implications are similarly important. The CDC recommends naloxone when an opioid overdose is suspected because it can reverse the opioid component, even when xylazine or another nonopioid sedative is suspected. Naloxone does not reverse xylazine’s direct effects; emergency medical assessment and supportive care remain necessary. The CDC has separately warned about severe medetomidine-associated withdrawal. These clinical considerations reinforce the value of knowing which substances are actually present in local drug markets.

What the study does not establish

Although the study includes thousands of observations across 17 states, its results should not be described as a nationally representative estimate of every fentanyl product. Samples were submitted through participating drug-checking and partner networks, so sampling patterns can influence observed trends. Likewise, a rise in detection is not by itself evidence that an adulterant causes a particular overdose or clinical presentation. These are different research questions that require different study designs.

The takeaway

The NIST findings show that fentanyl adulterants do not form a stable, predictable mixture. Xylazine, medetomidine, BTMPS and other additional substances can vary substantially with place and time. Forensic laboratories therefore need analytical methods that are both scientifically defensible and responsive to change. Rapid drug checking can provide early warning; validated confirmatory methods and careful case interpretation remain essential for evidential conclusions.

References and further reading

1. Sisco E, Pyfrom EM, Appley MG, Robinson EL, Beltran KA, Shuda SA. Trends in Fentanyl Adulteration From Rapid Drug Analysis and Research (RaDAR) Drug Checking Samples, January 2024 to June 2026. Drug Testing and Analysis. Published online October 7, 2026. https://doi.org/10.1002/dta.70164.
2. National Institute of Standards and Technology. NIST Study Shows How the Toxic Substances Mixed Into Fentanyl Vary Across the U.S. and Change Over Time. October 8, 2026. Read the NIST announcement.
3. NIST. Rapid Drug Analysis and Research (RaDAR): Providing Near Real-Time Insight into the Illicit Drug Landscape. Program and analytical workflow.
4. Centers for Disease Control and Prevention. Medetomidine Situation Summary. April 2, 2026. CDC guidance.
5. Centers for Disease Control and Prevention. Xylazine: What You Should Know. CDC overdose prevention guidance.

Editorial note: This article summarizes published research for forensic education and news reporting. It does not replace laboratory method validation or emergency medical guidance.