Skip to main content


No Science Behind Cannabis DUI Says Experts

May 10, 2016 11:33AM ● By Randy Robinson
Driving while high on cannabis has become a hot-button issue over the past few years. As more states permit legal marijuana, legislators have wrestled with how to combat "drugged driving," with little success.

In 2013, the Colorado state legislature passed HB 1261 to address these concerns, though the law didn't pass without some major problems. Currently, the THC DUI limit in Colorado is set at 5 ng/mL in the blood, an arbitrary value with no science behind it. As more states are poised to legalize in November, they, too, are considering a 5 ng/mL limit.

In a recent AP article, the American Automobile Association's CEO and president, Marshall Doney, concluded these DUI laws aren't helping anyone. "There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol," he said. "In the case of marijuana, this approach is flawed and not supported by scientific research."

In 2013, William Breathes, a pot critic and medical writer, set out to prove just how unscientific this limit was. He submitted two blood draws at a local lab: one before smoking and one after. The results showed his before-smoking THC levels were over 8 ng/mL above the limit, even though he wasn't impaired. 

How did Breathes, and many other non-impaired drivers cited for cannabis DUIs, exceed this limit while sober? THC is a fat-soluble molecule, meaning it dissolves in oil and gets stored in our fat. As we metabolize our fat cells throughout the day, we release small amounts of THC and its metabolites into our blood. Studies have shown THC can appear in our blood (and other fluids, such as urine and saliva) days if not months after we last consumed. At a meager 5 ng/mL limit, that means any cannabis consumer is technically committing a DUI when they get behind the wheel, even if they're stone-cold sober.

In contrast, alcohol is a water-soluble molecule. It dissolves in water and passes through our bodies relatively quickly. The science behind alcohol DUI limits is pretty sound. The problem is trying to translate alcohol limits to marijuana, which just doesn't work.

Mark Kleiman, a professor of criminal and drug policy at New York University, told the AP that cannabis intoxication and driving should be one of the least of our worries. He noted that although marijuana can double a driver's risk of crashing, other mundane activities present risks, too. For instance, noisy children in the backseat also doubles the risk of a crash. Talking on a hands-free cell phone while driving can quadruple the risk of a crash. 

In Colorado, cannabis DUIs have unfairly targeted patients and recreational consumers alike, but the fight is far from over. State laws permit anyone accused of a DUI to fight their charges so long as they can show there was no impairment.

Most surprisingly, Colorado juries have exercised their right to nullification at record levels since the state implemented its cannabis DUI policies. Under jury nullification, every American jury has the right to rule a verdict however they see fit, even if that means ignoring the law itself. Until better laws are enacted, this may be our only means to combat unfair DUI policies.