Reliable Cannabis Breathalyzer Remains Elusive for Researchers

Woman pulled over by police officer and taking a breath test

A reliable breathalyzer to detect recent cannabis use and impairment would be a critical tool for law enforcement officers, however, it does not currently exist according to a study published in the Journal of Breath Research.1

The researchers in the study, a collaboration between the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder, used an impaction filter device to collect breath aerosol samples from cannabis users one hour after cannabis use. The samples of the 18 study participants were evaluated using liquid chromatography with tandem mass spectrometry. During the study, a total of 42 breath samples were collected between November 2020 and May 2022. Cognitive and psychological tests of intoxication were also administered.

In order to get baseline values, samples were collected at 4 weeks and 15 minutes prior to use. The research team used a mobile laboratory to take blood and breath samples, and administer the battery of tests, which allowed them to evaluate study participants at set intervals without directly handling or administering the cannabis, which still remains illegal for researchers at the federal level. Study participants were instructed to purchase a specific strain of cannabis flower with 25% delta-tetrahydrocannabinol (THC) and smoke it in their home while the mobile unit parked outside their residence.

Study results revealed that although the breathalyzer was able to collect breath data and quantify THC levels, it could not reliably indicate whether a person had recently used cannabis.

The breathalyzer technology detected THC in 31% of baseline values 4 weeks before cannabis use, in 36% of baseline values 15 minutes before cannabis use, and in 80% of samples taken 1 hour after cannabis use. In 3 study participants, THC was not detected in breath or blood samples. Overall, the findings are similar to results seen in a handful of other studies with different devices, sampling methods, and varying patient characteristics.

“Our results do not support the idea that detecting THC in breath as a single measurement could reliably indicate recent cannabis use,” the authors of the study wrote. “In our pilot research, we found that in regular cannabis users, their breath around an hour after use is not looking a whole lot different than their baseline measure on days that they haven’t used at all,” said Cinnamon Bidwell, PhD, Assistant Professor in the Department of Psychology and Neuroscience at CU Boulder.2 When compared to alcohol breathalyzers, research from the NIST has previously shown that 1 million times more ethanol is released per single breath than THC exhaled in 12 breaths. THC is also lipophilic and often gets stored in adipose tissue leading to longer and non-uniform release into the bloodstream leading to complications correlating THC levels with recent cannabis use.


  1. Jeerage KM, Beuning CN, Friss AJ, Bidwell LC, Lovestead TM. THC in breath aerosols collected with an impaction filter device before and after legal-market product inhalation—a pilot study. J Breath Res. 2023;17(3):037103. doi:10.1088/1752-7163/acd410
  2. Marshall L. A reliable cannabis breathalyzer? Possible, but not easy. CU Boulder Today. Published September 11, 2023. Accessed September 18, 2023.