Federal researchers say breath-based cannabis testing is possible—but warn of limitations as new studies reveal THC detection even before ingestion
Federal scientists at the National Institute of Standards and Technology (NIST) have made a significant breakthrough by detecting THC—the main psychoactive compound in cannabis—in human breath following the consumption of infused edibles. This discovery, recently published in the Journal of Analytical Toxicology, represents a vital step toward developing cannabis breathalyzers for roadside and workplace testing.
Yet, researchers emphasize the limitations of their findings. “This is an important step forward,” said Jennifer Berry, NIST chemist and lead author. “But more research is needed to understand how THC behaves in the body and in breath over time.”
First breath-based THC eetection after edibles sparks hope—and questions
The research was a collaboration between NIST and the University of Colorado Anschutz Medical Campus. Involving 29 volunteers who consumed cannabis edibles of varying THC strengths (5 mg to 100 mg), the study used two distinct breath-collection methods at intervals of 47, 92, and 180 minutes post-ingestion.
Findings were mixed. While two-thirds of participants exhibited a rise in breath THC levels, others showed no change or even a decrease. Surprisingly, nearly all participants had detectable THC in their breath before consuming edibles, even after a requested 8–12-hour abstinence window. This residual presence raises questions about the reliability of one-time breath measurements to determine impairment.
Tara Lovestead, NIST chemical engineer, highlighted the potential utility of multiple breath tests over time, suggesting a broader testing window could help distinguish recent use from past consumption. However, Lovestead noted the urgent need for standardized devices and protocols, stating, “Those standards don’t yet exist.”
Cannabis breathalyzers: science or pseudoscience?
As cannabis legalization expands across states, the debate around THC detection intensifies. Many states use blood THC concentration as a measure of impairment, but NIST’s study—alongside others—casts doubt on this practice.
A 2023 review in The Lancet concluded there's “no linear relationship” between blood THC and impaired driving. Similarly, a DOJ official questioned the reliability of setting legal THC limits, noting that chronic users metabolize cannabis differently from occasional users.
Even earlier federal findings—from the National Highway Traffic Safety Administration—warned that “drug concentration in blood does not correlate to driving impairment,” a stark contrast to well-established alcohol limits.
The limitations in breath and blood testing point to a broader need for scientifically valid tools. Rutgers Law Professor William J. McNichol recently criticized roadside cannabis tests as “pseudoscientific,” calling for evidence-based reforms to transportation safety policy.
In September, NIST is expected to host a landmark workshop with device manufacturers to advance this technology. Findings will be compiled in a report aimed at shaping future breath-testing standards.
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