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Testing & Processing Cannabinoid analysis

Breath and Blood

The use of blood ∆9-THC levels as a marker of impairment (for example, in drivers) has been met with controversy. Previous studies have found mixed results, with many failing to reliably establish the link between THC blood concentration and impairment. To delve into the issue further, researchers from the Cancer Immunotherapy Research Institute, Roseville, California, investigated THC blood and exhaled breath concentrations and impairment (1).

The results showed that, even after a 12-hour abstinence period and in the absence of any impairment, most test subjects had THC blood concentrations exceeding the legal limits in place in five US states. The authors highlighted that a single measurement of THC blood concentration and a single measurement of exhaled breath are not enough to establish cannabis impairment.

Importantly, they also suggested that cannabigerol, cannabichromene, and tetrahydrocannabivarin – all of which were detected in breath only during the impairment window – may be the key to reliably measuring impairment. We spoke to Mike DeGregorio, one of the authors of the paper, to find out more.

What inspired this study?

While conducting a clinical trial for recent cannabis use testing, we discovered individuals who experienced wrongful discrimination in the workplace based on zero-tolerance or arbitrary THC limit policies. We were inspired by the unjustified use of these THC limits for legal and employment purposes. We hope that, in the future, individuals will be able to use cannabis responsibly without fear of false prosecution and wrongful termination.

Can you briefly describe how you analyzed THC blood and breath concentrations and impairment?

We collected blood and breath samples prior to smoking, immediately after smoking, and at multiple time intervals post-smoking. We then analyzed the concentrations of THC and other cannabinoids in blood and breath using standard and validated liquid chromatography high-resolution mass spectrometry (LC-HRMS) analytical methods.

For impairment, subjects were asked to smoke to the point where they felt they could no longer safely drive a car or until they felt incapacitated, whichever came first. They were then asked to rate their level of impairment at multiple time points post-smoking using a 10-point numerical Likert-type scale on which “0” represented no impairment and “10” represented maximal impairment or incapacitation for that individual. This self-rating system was then related to a physical measure of impairment known as horizontal gaze nystagmus, which is a component of sobriety testing.

Can you summarize your findings?

Our main findings were that single measurements of THC concentrations in blood or breath were not correlated with impairment and that more frequent users had THC levels above any limits at baseline. They also exhibited shorter durations of impairment, which is consistent with drug-induced tolerance. We concluded that multiple parameters are needed to assess cannabis-induced impairment.

Do you think we need new methods of measuring THC impairment?

I think it’s fair to say there is unanimous agreement that new methods of determining THC impairment are needed. Single measurements of THC alone will likely never be enough to reliably establish impairment. Looking at key pharmacologic indicators associated with impairment will most likely be required. A combination of physical evidence of impairment and an accurate analytical test that determines recent cannabis use is a better way to assess cannabis-induced impairment.

Do you have any plans for further studies?

Our ongoing studies address the unmet need for a simple test that provides a positive result only during the impairment window. A field trial of our comprehensive blood-breath test that confirms recent use of edible or inhaled cannabis will be conducted in the future. If successful, this will allow individuals to use cannabis responsibly without fear of being wrongfully terminated or prosecuted.

Image credit : National Cancer Institute /

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  1. Wurz & DeGregorio, Scientific reports, 12(1), 1 (2022). DOI: 10.1038/s41598-022-11481-5. 
About the Author
Margot Lespade

Margot Lespade, Associate Editor, The Cannabis Scientist

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