Report: State shouldn’t set driving limit for pot

Marijuana in MI

GRAND RAPIDS, Mich. (WOOD) — A state commission found Michigan should not set a limit on how much THC drivers can have in their system before they’re deemed impaired.

THC is the main chemical responsible for marijuana’s psychoactive effects.

The Impaired Driving Safety Commission, a six-member panel mandated by state law to research and recommend a scientifically-supported THC threshold, released its report (PDF) Friday.

The commission, whose members were appointed by former Gov. Rick Snyder, includes a representative from the Michigan State Police, a registered medical marijuana patient, a forensic toxicologist, a licensed physician and two university professors with expertise in the areas of traffic safety and cannabis pharmacology and toxicology.

“Based on the total body of knowledge presently available, the Commission finds there is no scientifically supported threshold of THC bodily content that would be indicative of impaired driving,” the report reads in part. “There is a poor correlation between driving impairment and the blood (plasma) levels of THC at the time of blood collection.”

>>Inside woodtv.com: Marijuana in Michigan

According to the commission, THC levels in blood drop rapidly, but impairment happens more slowly and peaks after blood levels have already dropped. Additionally, level of impairment varies based on prior usage.

“The implications of tolerance to cannabis are that lower blood THC levels in infrequent users may result in impairment that would only be experienced at higher THC levels by regular cannabis users,” the report’s authors wrote. “Therefore, because there is a poor correlation between THC bodily content and driving impairment, the Commission recommends against the establishment of a threshold of THC bodily content for determining driving impairment and instead recommends the use of a roadside sobriety test(s) to determine whether a driver is impaired.”


According to the commission’s report, of the 33 states that have legalized both recreational and medical marijuana, six have adopted impaired driving per se thresholds of THC bodily content in blood:

  • Colorado: 5 ng/ml
  • Montana: 5 ng/ml
  • Nevada: 2 ng/ml
  • Ohio: 2 ng/ml
  • Pennsylvania: 1 ng/ml
  • Washington: 5 ng/ml

24 Hour News 8 reached out to law enforcement and defense attorneys for reaction to the Commission’s recommendation against setting a per se limit for Michigan.

“I was surprised to be honest,” said Jeff Crampton, a longtime criminal defense attorney in Grand Rapids who applauded the commission’s decision. “I didn’t think they’d do the right thing. … There’s a lot of politics with this.”

Kent County Prosecutor Chris Becker also agreed with the commission’s determination.

“There is no science behind (setting a limit),” Becker said in an interview from his office on Ionia Avenue NW. “From a prosecutor’s perspective, we want science. We want a reason to have a number and just to make one up to make us all feel better, I don’t support that.”

A Kent County sheriff’s deputy who’s specially trained in drug recognition commended the commission’s decision as well.

“THC from marijuana acts very differently than alcohol does,” Deputy Ryan Dannenberg explained.

“When you’re at your peak level of alcohol, it’s also generally your peak level of impairment. So when you’re drunkest, that’s also the worst driving you’re going to have. With THC it’s just not the same. … Your THC level in your blood might be way up here,” Dannenberg continued, holding his hand high, “but your impairment level’s only down here at this point. As your body starts to get rid of that THC, now your impairment level is up here. So it just doesn’t match. It doesn’t correspond well. …  If we set a limit, and we’re catching people who aren’t high and letting go people who are, that’s not good for anybody.”

The downside of not setting a THC limit, said Becker, is lack of uniformity in how the impaired driving law is administered from county to count across the state.

“Consistency is kind of out the window,” Becker said. “At least with alcohol, .08 is in Detroit, and .08 is in Chippewa County. It’s some level of consistency.”

Becker expects more impaired driving suspects to go to trial instead of pleading because with no set limit, they can argue their blood THC level did not cause impairment. Law enforcement will have to use results of field sobriety testing and witness statements to build their cases.

“Like the old days of alcohol before you had a breath test,” Becker said. “You just had to base your case on the driving, field sobriety, all the facts and circumstances the witnesses could see at the time. We’re going to that for marijuana now.”

Dannenberg said it will take more effort from law enforcement, but he welcomes that.

“We’re willing to do the hard work. We want to find people who are making our roads less safe,” he said. “We’re not looking for people who smoked weed last week or yesterday. That’s not what we’re about. We’re about people who are endangering our roadways, finding those people and getting them off the road to make sure everybody can travel safely.”

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