To deter impaired driving in areas where marijuana use is legal, several jurisdictions have set per se limits ranging from 2 to 5 nanograms of THC per milliliter in motorists’ blood. New research, however, finds no evidence that drivers whose blood samples tested in that range are more likely to cause a traffic accident.
The study, published last month in the journal Addiction by a team of Canadian researchers, supports a key message relayed in a recent U.S. Congressional Research Service report on marijuana’s impact on driving: That is, experts aren’t convinced yet that cannabis use is associated with a higher risk of crashes.
“In this multi-site observational study of non-fatally injured drivers,” the study’s authors write, “we found no increase in crash risk, after adjustment for age, sex, and use of other impairing substances, in drivers with THC5ng/mL.”
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