Michigan state police say tests intended to detect THC in blood aren’t working, and haven’t for years. Several thousand criminal cases may be impacted by the revelation.

The agency has halted further blood toxicology testing for THC until a third-party, accredited lab can be hired, or the problem is resolved.

State police have not revealed what they believe caused the problem but say it’s existed since at least March 2019. The issue with faulty THC results was identified on Aug. 19 and prosecutors across the state were notified on Aug. 25.

State police say the testing method that was in use caused cannabidiol, better known as CBD, a non-psychoactive compound in cannabis, to show up in test results as THC, the intoxicating compound in marijuana.

“After further review, we now believe this discrepancy may impact cases that occurred on or after March 28, 2019, where the alleged violation is based on the finding of THC alone and there is insufficient evidence of impairment, intoxication, or recent use of marijuana to otherwise support the charged offense,” state police said in a statement issued Wednesday, Aug. 31.

State police only tabulated the number tests conducted since March 28, 2019, the date state police said CBD was made legal in Michigan.