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It used to be the stuff of stoner comedies and “Just Say No” campaigns. Today, marijuana is becoming mainstream as voters across the country approve ballot questions for legalization or medical use.
In response, state governments are testing ways to ensure that the integration of this once-illicit substance into everyday life doesn’t create new public health risks. These efforts are sparking a difficult question: At what point does marijuana driving mean someone is too high to get behind the wheel?
The answer is complicated. Brain scientists and pharmacologists don’t know how to measure if and to what extent marijuana causes impairment.
The reason: Existing blood and urine tests can detect marijuana use, but, because traces of the drug stay in the human body for a long time, those tests can’t specify whether the use occurred earlier that day or that month. They also don’t indicate the level at which a driver would be considered “under the influence.”
“It’s a really hard problem,” said Keith Humphreys, a psychiatry professor and drug policy expert at Stanford University in California, the first state to legalize medical marijuana and where recreational pot use among adults became legal in 2016. “We don’t really have good evidence — even if we know someone has been using — [to gauge] what their level of impairment is.”
Quick, how much marijuana can you legally smoke before you drive?
If you’re like a majority of Californians, odds are you don’t know the answer to that question. Nearly half, 46 percent, who responded to a recent survey from Eaze, an online cannabis marketplace, were unable to answer whether there exists a legal bloodstream concentration limit for THC, as there is for alcohol (there isn’t).
The online survey of 527 licensed Californian drivers, who all used cannabis within 30 days of responding, shows that “few know critical details about cannabis consumption and driving,” according to the executive summary.
Though a clear majority, 81 percent, were aware that it is illegal to drive under the influence of cannabis, a majority, 62 percent, also were unaware of the legal penalties that come with it. Like a DUI involving alcohol, they can include fines, jail time and license suspensions.