NIST: 4,563 drug residue samples from 2024–2026 analysed by DART-MS mass spectrometry — fentanyl adulterants are increasing (now more often six or more per sample), and xylazine is being displaced by medetomidine
On 8 October 2026 the US National Institute of Standards and Technology (NIST) described the results of a 2.5-year study showing how adulterants in illicit fentanyl change over time and differ between the eastern and western United States. A total of 4,563 drug residue samples collected nationwide between January 2024 and June 2026 were analysed; the work was published in the journal Drug Testing and Analysis.
- Technique: Direct Analysis in Real Time Mass Spectrometry (DART-MS) creates a unique “fingerprint” of each compound in a sample and reveals all components, including trace adulterants, within seconds. According to NIST, conventional mass spectrometry systems in forensic and public health laboratories take tens of minutes, because the material must be vaporised and pass through a column with a special coating.
- Findings: adulterants rise and fall in prevalence cyclically, each independently of the others. Animal tranquillisers such as xylazine are much more common on the East Coast than in the West; xylazine is being displaced by medetomidine, a much more potent sedative that can cause severe withdrawal symptoms. The industrial chemical BTMPS, used in manufacturing plastics, has appeared in fentanyl samples in both the east and the west since the summer of 2024.
- Samples from the western part of the country tend to contain fewer adulterants, but in higher concentrations than in the east. The number of adulterants is rising: in early 2024 one or two were typically found in a sample, whereas six or more compounds are now more common. According to the study’s author, more adulterants make it harder both to analyse a sample and to treat an overdose.
- The study is part of the Rapid Drug Analysis and Research (RaDAR) programme, in which NIST works with partners in public health, law enforcement, forensic science and medical examiner offices. The team is modelling how adulterants move between regions — for example from Philadelphia to Delaware and Maryland and then west — is planning a similar survey of adulterants in ketamine, and is investigating adulterants in a new class of opioids, orphines, some of which are more potent than fentanyl.