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Cannabis and Driving: How Much Is Too Much?

Cannabis and Driving: How Much Is Too Much?


Cannabis and Driving: How Much Is Too Much?

You won’t believe how much is too much when it comes to cannabis and driving.

More and more states are considering making the move to legal recreational cannabis for adults, and that’s creating a challenge for lawmakers. They wonder how much is too much when it comes to cannabis and driving.

When someone’s driving under the influence of alcohol, it doesn’t take much to determine how drunk they are. There’s a simple, straightforward cutoff. If the driver has a blood-alcohol level of 0.08 percent or more, that driver is illegally impaired.

But knowing how THC affects cannabis and driving is much harder, blood tests are an unreliable way to judge someone’s impairment from using marijuana.

So when a new study came out blasting the link between THC in the blood and driver impairment, lawmakers were left scratching their heads.

That’s because the study, ordered by the AAA Foundation for Traffic Safety, found that measuring impairment by measuring the level of THC in someone’s blood is not supported by the science at all.

And today, there are laws on the books in six states that judge driver impairment by measuring exactly that: THC in the blood.

“There is no concentration of the drug that allows us to reliably predict that someone is impaired behind the wheel in the way that we can with alcohol,” according to Jake Nelson, AAA’s director of traffic safety advocacy and research.

That difficulty creates significant obstacles for keeping impaired drivers off the road. In the wake of the AAA study, lawmakers have to understand that alcohol and cannabis affect the body in very different ways.

Put simply; you’re drunk when alcohol makes it into your bloodstream. But THC in your blood doesn’t make you high. That only happens when the cannabinoids make it to the fatty tissue in your brain.

Take regular cannabis users, for instance. This includes anyone who takes the drug as a medicine. These users often show absolutely zero signs of impairment, but the level of THC in their blood would make them “illegal” drivers in some states.


Cannabis can stay in the blood for hours, days, and sometimes even weeks after the effects of being stoned wear off.

But the idea that THC in the blood is making drivers impaired has led to a whole range of mistaken ideas that are skewing our understanding of legal cannabis’ effect on public health.

For now, then, the question for responsible legislators is figuring out exactly how much is too much when it comes to cannabis and driving.

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