BOSTON (WBZ NewsRadio) — Michigan’s Impaired Driving Safety Commission is recommending "no legal limit" for how much marijuana a person can have in their body while driving. According to its report, levels of THC (the intoxicating compound in cannabis) does not correlate well to actual levels of intoxication.
The committee has spent two years studying how cannabis consumption affects people behind the wheel. While it determined that using cannabis can have an effect on drivers, it concluded that blood-THC levels have “very poor correlation” to impairment levels. Instead, the panel says, roadside sobriety tests work best.
Here’s why: If you eat a cannabis edible, the THC is metabolized through enzymes in the liver. That process takes a long time, and the high takes a few hours to kick in. Someone could feasibly eat a pot brownie, drive 20 minutes, and safely get to their destination before the intoxication has a chance to take effect (some THC, driver NOT intoxicated).
However, smoking or vaporizing cannabis almost immediately introduces THC to the bloodstream, making blood-THC levels quickly spike and the user feel high within one to five minutes. But within ten minutes, those inhaled THC levels drop to half their peak. That rapid fluctuation means if a driver has smoked, when their blood is tested, it will not accurately reflect their blood-THC level at the time of the alleged driving offense (some THC, driver VERY intoxicated).
Another reason blood-THC levels are not a good indicator of impairment is that each body metabolizes cannabis at a different rate. While some people will be well over the high within an hour, others will feel it until they wake up the next day. Then there’s the fact that heavy cannabis users basically have high levels of THC in their blood all the time, because it stores in their fat cells. But they will not always be intoxicated. There is even a level of tolerance a daily user can reach where no matter the level of THC they ingest, they can no longer feel the high (lots of THC, driver NOT intoxicated).
Add to that—as anyone taking a urine test will tell you—the fact that THC levels can linger in your system for thirty days after cannabis has been ingested (some THC, driver stone-cold sober!) and you can start to see why enforcing a standard measurable blood-THC limit may not help decrease impaired driving at all.
The Commission’s report even found that stoned drivers are less dangerous than drunk drivers. It says “cannabis impaired subjects typically drive slower, keep greater following distances, and take fewer risks than when sober,” whereas alcohol makes people “drive faster, follow more closely, and take more risks than when sober.”
The report concludes that THC levels are “indicative of exposure, but are not a reliable indicator of whether an individual is impaired.”
The report, along with recommended next steps, have been sent to Michigan’s Governor Gretchen Whitmer. The state’s legislature decides what happens next.
Blunt Talk is a podcast about cannabis hosted by Brit Smith every Monday. You can listen to all previous podcasts on iHeartRadio.