It's illegal to drive under the influence of marijuana in Michigan, but there is no established limit. (Courtesy/Michigan State Police)
It's illegal to drive under the influence of marijuana in Michigan, but there is no established limit. (Courtesy/Michigan State Police)

DETROIT—The Michigan State Police crime lab has stopped screening blood samples for THC, the compound that gives marijuana users a high, after problems with testing, a spokeswoman said.

County prosecutors were informed this week, Shanon Banner told The Associated Press.

The suspension will be in place “as we work to learn more and/or until we can institute another validated method of testing to ensure accuracy,” Banner said in an email.

Since 2018, marijuana has been legal under state law for people who are at least 21. Medicinal use was approved 10 years earlier. It’s still illegal to drive under the influence of marijuana but Michigan, unlike some other states, has no established limit.

In 2019, a commission recommended against creating a threshold because of a “poor correlation” between bodily content and driving impairment. Still, those blood tests have been used by authorities to detect the presence of THC while investigating and requesting charges in drugged driving cases.

Banner said a “discrepancy” in the lab was discovered this week in which the presence of CBD may have led to a positive result for THC. CBD, also found in marijuana, does not cause a high and is often sold as a dietary supplement or included in creams and other personal care products. CBD products are legal, with some restrictions, in almost all states. Tests have been halted until the testing issue is resolved.

“We are actively working to identify the scope, but likely won’t have additional information until next week,” Banner said.

On Monday, Ingham County Prosecutor Carol Siemon announced that her office would no longer rely on Michigan State Police laboratory testing to prove toxicology results regarding marijuana use in criminal cases. Her office is also actively reviewing past convictions involving possibly unreliable testing results.

‘Gander Editor Kyle Kaminski contributed to this report.