Cannabis and Cars | Michigan Impaired Driving Safety Commission Rejects THC Driving Limits


In 2016, Michigan lawmakers created the Impaired Driving Safety Commission within the Michigan Department of State Police to research and recommend whether there should be a per se threshold of THC (the main psychoactive ingredient in marijuana) for purposes of drugged driving—similar to the 0.08 Blood Alcohol Content (BAC) threshold that we have for drunk driving. The Commission was composed of members of the Michigan State Police, a medical marijuana patient, a forensic toxicologist, a physician, and professors from Michigan universities with expertise in traffic safety and cannabis pharmacology and toxicology.

The Commission was tasked with determining whether there is scientific support for establishing a THC limit that would make it a crime to operate a vehicle with that amount of THC in your bloodstream. On March 26, 2019, the Commission concluded its report with the recommendation that there is no scientific basis for establishing a specific THC limit that would constitute impairment for purposes of drugged driving.

In other words, the Commission concluded that having more THC in your bloodstream does not necessarily mean that you are more stoned. This is dramatically different from alcohol because a person’s blood alcohol content correlates with impairment—so the more alcohol you consume, your blood alcohol content increases, and your level of intoxication also increases. However, the human body metabolizes THC in a different way and because THC is fat soluble (meaning that it gets absorbed into fat cells in the body), a person can have significant levels of THC in his or her bloodstream for significant periods of time after their last use and long after the impairment has worn off.

In many ways, the Impaired Driving Safety Commission’s report confirms the findings of a similar federal study conducted by the National Highway Traffic Safety Administration in July 2017. NHTSA also concluded that THC levels in the bloodstream do not correlate with impairment.

The Impaired Driving Safety Commission’s report also contained several other very interesting findings. While the science shows that cannabis use impairs some of the functions associated with driving a vehicle, studies have shown that drivers that have consumed cannabis are subjectively aware of their impairment and compensate for their impairment by driving slower, keeping greater following distances, and taking fewer risks than they would driving sober. This is a dramatic contrast from drivers under the influence of alcohol who typically drive faster, follow more closely, and take greater risks.

Under Michigan law, it’s illegal to operate a vehicle if your ability to drive is impaired by alcohol, a controlled substance, or any other intoxicating substance (including legal prescription or over the counter medications). If you decide to consume cannabis, alcohol, or another substance that may impair your ability to drive, the best practice is to find a sober driver. If you are charged with operating under the influence of marijuana, contact the experienced marijuana law attorneys at Grewal Law PLLC for a free consultation today.

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