A recent Michigan Supreme Court ruling makes it more difficult to prove drugged-driving cases involving marijuana.

The high court overturned a 2006 ruling that 11-carboxy-THC — a long-lasting byproduct of metabolism created when the body breaks down the psychoactive ingredient of marijuana — is a schedule 1 controlled substance, a drug classification that includes heroin.

Now, prosecutors will have to prove drivers had the actual narcotic or its active ingredient in their systems at the time they are alleged to have been driving while drugged.

Previously, people could have been charged with a driving offense involving drugs long after they had ingested or inhaled marijuana because the metabolite remains in the body for a month after use.

Defense lawyer Jerry Engle said this means people who were convicted since 2006 of drugged-driving based on a finding of the metabolite should be talking to a lawyer. Their convictions could be set aside, he said.

In Jackson County, there might have been 100 such cases, he said.

Jerrold Schrotenboer, Jackson County’s chief appellate attorney, is not so sure. “I am not particularly concerned about a flood of overturned convictions or motions,” he said.

Operating with the presence of a controlled substance in the body is a misdemeanor and people only have six months to challenge a misdemeanor, he said.

The two lawyers argued the topic of 11-carboxy-THC before the Supreme Court in January 2006, after which the court made the ruling it recently overturned.

At issue were cases from Jackson and Grand Traverse counties. The local case involved the prosecution of Dennis Kurts for driving with marijuana in his system.

Blackman Township police in February 2004 cited Kurts, 44, of Michigan Center after he was stopped for driving erratically. He admitted smoking pot, but a blood test did not detect the narcotic THC, or tetrahydrocannabinol, which is in marijuana. It did show the presence of carboxy THC.

The most recent Supreme Court ruling stemmed from a 2005 Washtenaw County case. George Evan Feezel was traveling on Packard Road in Ypsilanti Township when his vehicle struck and killed pedestrian Kevin Bass.

Feezel was legally drunk and had 11-carboxy-THC in his blood. He was charged with several offenses, including drugged driving causing death.

Based on its ruling about the metabolite, the high court vacated the drugged-driving conviction and remanded case to the Washtenaw County Circuit Court.

This could be considered a victory for those who use marijuana for medical reasons, which Michigan voters legalized in 2008.

“(The Supreme Court) had to change the law, or everyone who takes medical marijuana could not drive a car,” Engle said.

Before, legal marijuana users would have to worry about being caught with the metabolite in their bodies well beyond the time they could feel the drug’s effects.

“The threat of a sick person not being able to drive because of a health decision was beyond the scope of reason,” Joe Cain, chief operating officer for the Michigan Medical Marijuana Association, wrote in an e-mail. He said the law was being used as a “weapon against the innocent.”

Schrotenboer pointed out, however, the existence of the metabolite still can be used as circumstantial evidence of drug use. Calling 11-carboxy-THC a controlled substance makes prosecution “really, really easy,” he said.

“Otherwise, it is a little bit harder.”

Under the drugged-driving statute, only the presence of a drug has to be proven, not a quantity, as is required with drunken driving.

“Hopefully prosecutors will not look for another exploit of our law, but will try to only prosecute those who are truly impaired,” Cain wrote.