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The difficulties of setting a legal limit for high driving in Michigan

The Michigan Court of Appeals ruled on a medical marijuana case today.
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The Michigan Court of Appeals ruled on a medical marijuana case today.

On Tuesday, the Michigan Supreme Court ruled that medical marijuana patients are not automatically breaking the law if caught driving after using marijuana.

Passed in 2008 by Michigan voters, the state’s Medical Marihuana Act does prohibit patients from operating a motor vehicle while under the influence of pot.

But the law fails to explicitly say just how much THC, marijuana’s active ingredient, needs to be in the bloodstream for a user to be considered “under the influence.”

Which is why the justices offered this piece of advice to lawmakers: Set a legal limit for pot consumption, just like the blood alcohol content metric for alcohol intoxication.

“This case could have been easily resolved if the (law) had provided a definition of 'under the influence,' " the justices said on Tuesday.

But in other states that have legalized marijuana in some form or another, setting a DUI statute for pot hasn’t been easy.

“The question of a legal limit for marijuana is a vexing problem for public policy,” said Allen F. St. Pierre, the executive director of NORML, a drug reform advocacy group.

"...we just don't have that science for marijuana."

“We’ve been building research on the BAC for over half a century. But we just don’t have that science for marijuana.”

But even in the face of threadbare statistics, legislators across the country have started setting limits to marijuana use while behind the wheel.

In Washington state, where voters approved legalized marijuana use in 2012, a driver with five nanograms or more of THC per milliliter of blood is considered under the influence.

A few studies have advocated for the five nanogram limit, but not without contention.

First, for frequent pot smokers — including many medical marijuana patients — a built-up tolerance to the drug could skew the correlation between high THC levels and impairment. A blood test could reveal a level of THC over an imposed limit, but may not indicate poor driving abilities.

"[It] is going to cause a lot of impaired drivers to be missed and it's going to cause a lot of innocent people to get arrested."

In a recent Wall Street Journal article, R. Andrew Sewell, an assistant professor of psychiatry at Yale School of Medicine said that imposing such levels without comprehensive research could be a mistake:

"[It] is going to cause a lot of impaired drivers to be missed and it's going to cause a lot of innocent people to get arrested.”

Additionally, St. Pierre of NORML argues that police officers are often hesitant to administer blood tests due to “liability issues.”

“A roadside sobriety test is naturally much less invasive (than a blood or urine test), but even that’s not sorted out for marijuana yet,” St. Pierre said.

According to WSJ, a sobriety test for drugged drivers — similar to those existing for drunk drivers — does exist, but “just 6,837, or less than 1%, of the nation's police officers are fully trained, according to the International Association of Chiefs of Police.”

Where current methods for testing drugged driving fail, technology might pick up the slack. In December, Amar Toor of The Verge reported new approaches in the works, including a British startup’s fingerprint scanner that can detect THC in sweat.

But as Toor reported, it could be awhile before those technologies reach the States:

“The fingerprint scanner won't be ready for market until the end of 2013, and although the company has signed a deal to distribute its product in the US, it would still need to receive FDA approval before being used as a law enforcement tool.”

Earlier this year, CNN took the question of stoned driving to the streets, taking three pot smokers — the rare smoker, the occasional smoker, and the daily user — on a driving test to see if they would catch the eyes of cops after toking. Check out the results:


- Melanie Kruvelis, Michigan Radio Newsroom

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