Ask Dr. Dave: Does marijuana in my blood make me an impaired driver?

Dear Dr. Dave,

My husband was in a car accident that occurred at 5 p.m. He hadn’t smoked since the night before, at around 9pm. The police charged him with driving under the influence of marijuana, although he hadn’t smoked since 20 hours prior. Will he still test positive with active THC on the blood they took?

-Alinda in Arizona

Dear Alinda,

The mere presence of THC or its metabolites is not indicative of impairment. It indicates relatively recent use. According to the National High Traffic Safety Administration (NHTSA), cannabis does not increase accident risk. Some studies show that cannabis actually lowers accident risk.

The NHTSA says if one is “impaired” from cannabis they drive slower and more carefully. The FDA gives the standard psychoactive drug warning for Marinol, or synthetic THC, which has been FDA approved and on the market since 1986, “Warning: Don’t drive, operate heavy equipment or engage in dangerous activity until you determine if it interferes with those activities. Some consumers of cannabis don’t have trouble driving, and in some cases, their driving improves.

Feel free to have your husband’s lawyer give me a call to discuss the science and the possibility of expert witnessing.

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About the Author

David Bearman, M.D.

Dr. Bearman is one of the most clinically knowledgeable physicians in the U.S. in the field of medicinal marijuana. He has spent 40 years working in substance and drug abuse treatment and prevention programs. Dr. Bearman was a pioneer in the free and community clinic movement. His career includes public health, administrative medicine, provision of primary care, pain management and cannabinology.