Lawmaker wants blood levels of THC to determine whether drivers are impaired by marijuana


(Photo by Justin Sullivan/Getty Images)

LANSING, Mich. (WLNS) – A Lansing lawmaker wants the state to rely on THC levels in a driver’s blood to determine if they are impaired by marijuana.

Delta 9-tetrahydrocannabinol, commonly called ∆9-THC or simply THC, is the main psychoactive ingredient in cannabis. Determining when someone is impaired by it has been a major challenge as states decriminalize marijuana.

The bill introduced by Republican State Representative Pamela Hornberger would make it a crime to drive with THC levels above 5 nanograms per milliliter of blood.

That limit would apply the same limits to the compounds 11-OH-THC and THC-COOH, which are metabolites of ∆9-THC. That means your body breaks THC down into those compounds over time.

Those chemicals can remain in your body days or weeks after exposure to marijuana, long after the impairing effects have worn off. They are also fat-soluble, meaning they can build up in a cannabis user’s fat over time and be gradually released into their blood.

A March 2019 report from Michigan’s Impaired Driving Safety Commission found that blood levels of ∆9-THC are not a reliable indicator of whether a driver is impaired. Click here to read the report. The relevant statement can be found at the bottom of page 6.

Under Hornberger’s bill, driving with too much THC or its related chemicals in your blood could be punished by 360 hours of community service, 93 days in jail, and/or a fine of $100 to $500.

The bill has been referred to the State House Committee on Rules and Competitiveness. Click here to read the text for yourself. The changes are on page 8.

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