A research team at Virginia Commonwealth University has introduced a prototype for a THC breathalyzer that could bring roadside marijuana testing closer to practical use.
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Studies have shown that frequent users can have higher baseline THC levels without impairment, while occasional users may be more affected at lower concentrations.
“So the same effect level… will be correlated with a very different concentration of THC in the blood of a chronic user versus an infrequent user,” one researcher noted.
Additional studies have further complicated the issue. A 2019 study found drivers at legal THC limits were not statistically more likely to be involved in crashes, while a report from the National Highway Traffic Safety Administration concluded that “relatively little research supports” a link between THC levels and crash risk.
Unlike alcohol, the agency said, drug concentrations in blood do not align with impairment in the same way alcohol does.