Commission: Michigan Should Not Set THC Limit For Drivers

smoking marijuana
Photo credit (Dreamstime)

LANSING (WWJ) - A state commission says Michigan should not set a legal limit for how much THC, marijuana's active ingredient, motorists can have in their system.

The Impaired Driving Safety Commission last week forwarded its findings to Gov. Gretchen Whitmer and the Legislature after spending about a year-and-a-half studying how marijuana affects drivers.

The panel recommended that Michigan not set a limit for the amount of marijuana's active ingredient is in a motorist's blood, according to Commissioner Margeaux Bruner; instead recommending that the state continue to use roadside sobriety tests to determine if a driver is impaired. 


As for why, the report states that -- unlike with alcohol -- levels of tetrahydrocannabinol (THC) in a person's blood are not a "reliable indicator" of whether they're impaired.

"With alcohol there's a .08 (BAC) limit, and if you are .08 you are considered impaired," Bruner told WWJ's Michael Cohen. "Now, two people, it might taken them a different amount of consumption to reach that .08; but we agree that once you reach that .08 you are compromised.

"It is not the same at all with THC at all," she said, "because it's stored in the fat and not the blood. So a person with a higher metabolism would excrete it from the body much more quickly than a person with a slower metabolism."

How the marijuana was consumed is also factor, she said, in how soon the effects from the pot dissipate. 

"With alcohol, pretty much we're all drinking it in liquid form," Bruner said. "If you're talking about THC, you can smoke it, you can vape it, you can eat it, you can put it on your body as a topical; in which case it would not cross the bloodstream and impair you at all."

"It also varies based on how much you consume, how habitually you consume. There are so many variations that make it completely different scientifically than alcohol. You're not comparing apples and apples."

Bruner said while other states with legalized recreational marijuana have set a THC limit, ranging from 1 to 5 nanograms (ng), "We decided to go in a different direction."

Having received the commission's recommendation, it's now up to the legislature to take any further action.

Michigan approved medical marijuana use in 2008, and recreational marijuana use last year. Under the law, users can have up to 2.5 ounces (71 grams) of the drug on them and up to 10 ounces (284 grams) at home and grow up to 12 plants.

It remains against the law the use marijuana it in a public place, or drive under the influence. 

pilot program, recently expanded statewide, allows specially trained police officer to ask to swab drivers' mouths and use a portable saliva-testing device to determine if they've been using drugs, including marijuana.