The NIDA Blog Team
October 20 2014

You already know the dangers of using marijuana before driving: Marijuana seriously impairs your motor skills and clouds your perception and judgment, all of which you need to safely operate a car. That’s why it’s illegal to drive high. But lots of people don’t know this … or they know it, but figure it’s okay “just this one time.” Whatever the case, it’s breaking the law, just like driving after drinking alcohol.

Driving under the influence of marijuana is a big problem. A 2007 study by the National Highway Transportation Safety Administration found that 8.7 percent of people driving at night on a weekend had been using marijuana—4 times the percentage of drivers who had had enough alcohol to impair them.

With all of these drugged drivers, police need an easy test to check if people have been using marijuana, like they have for alcohol. Unfortunately, there isn’t one—yet.

A Marijuana Breathalyzer

With alcohol, police can test a driver’s breath and tell if the person has enough in their system to impair their driving—a device called a breathalyzer. This works because alcohol leaves the body quickly.  This also means that the breathalyzer only measures alcohol that has been recently used.

Measuring marijuana, however, turns out to be way, way more complicated.

For one thing, marijuana can stick around in a person’s body a lot longer than alcohol. It can be detected in blood tests of heavy users as much as a month after they’ve stopped using it! So in theory, heavy marijuana users could test positive in a blood test for marijuana even if they haven’t used it in a few weeks.

Another tricky thing with marijuana is that, after taking it, frequent users may show a higher amount of THC (marijuana’s active ingredient) in their body fluids than infrequent users do, even if the effect on their driving abilities is similar.

This means there’s a big need for a test that can universally tell when a person has consumed marijuana during the previous few hours, when it can have its biggest impact on driving ability—whether or not he or she uses the drug frequently or just occasionally. It also needs to be easy to use by police and painless for drivers.

Scientists are hard at work on the problem, and last fall a team of researchers at NIDA’s Intramural Research Program had a breakthrough: a first successful test of a marijuana breathalyzer.

Getting High for Science

In their research study, the scientists had a group of frequent marijuana-using adults and a comparison group of occasional marijuana-using adults each smoke a single marijuana cigarette (with an exactly measured dose of THC) and then provide breath samples using a device called SensAbues. Both groups tested positive up to an hour later, and frequent users tested positive 2 hours later.

So far it’s not perfect, and even though the collection device is very portable, the equipment to test the results isn’t, so there are still some hurdles. But it’s one step closer to making the roads safer from drugged drivers.

Tell us what you think in comments: Do you think if the police had a marijuana breath test, it would deter people from using marijuana before driving?

Check out these PSAs from Colorado reminding residents that while recreational use of marijuana is legal—driving under the influence of marijuana is illegal.

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