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Cops Test New Weed Breathalyzer On California Drivers

This could change the face of DUIs in the country.
Image: Wikimedia

Your days tooling around town, hotboxing the car may be numbered. While driving impaired under the influence of marijuana has always been illegal, law enforcement and policy makers have had yet to arrive at a standard measurement to prove impairment. A new marijuana breathalyzer that immediately detects THC levels could bring them one step closer to regulating marijuana-related impairment on the roads.


During an initial field test of the breathalyzer, California police officers teamed up with Mike Lynn, CEO of Hound Labs, which developed the device, to pull over erratic drivers and ask them to voluntarily blow into the breathalyzer. Purely for testing purposes, the drivers didn't face arrest unless they were also drunk (one of whom was). A handful of drivers even admitted to smoking weed within a half hour or several hours of driving. And those who tested positive for THC were given safe rides home.

Unlike breathalyzers that may simply detect the presence of THC, the Hound Labs device detects the levels of THC in parts per trillion. "That gives us a very precise amount of THC in the breath. That number, that measured level will ultimately be correlated to driving impairment at roadside," Lynn said. "Any legislation related to impairment needs to reflect true data."

Image: Courtesy of Hound Labs

It's not clear exactly how much THC, the main psychoactive compound in cannabis, leads to impairment, but one study showed that drivers under the influence of marijuana had increased weaving with levels 13.1ug/L (micrograms/liter) THC.

In the next phase of testing, people will be given marijuana and then asked to drive around a safe, enclosed space so researchers can determine at what level impairment begins. THC in the breath only shows up within about the first two hours after people smoke, Lynn explained. "You can smoke every day, but if you haven't smoked for a few hours we're not going to detect it and measure it. That's the time period that correlates with maximum impairment," he said.


"It's critical for protecting people who have the legal right to smoke cannabis. Whatever you did last night shouldn't frankly impact you getting arrested the next morning if you're not impaired. That's the problem with urine, blood, and saliva tests."

Under the current model, if a driver is pulled over for seeming impairment, but doesn't test positive for alcohol, police officers can still make an arrest and order a THC test. In most places, if you refuse to take the test, you can lose your license for a year. Experts usually advise that if you haven't used marijuana for at least three days, to choose the blood test, usually the most accurate, because THC is detectable in the blood from two to seven days. Otherwise, they often say to choose a urine test because it shows THC from up to 35 days prior. But even so, detecting THC alone is not enough to prove impairment, which is required for DUI convictions.

"It's critical for protecting people who have the legal right to smoke cannabis."

The Hound Lab breathalyzer doesn't only measure THC in the breath, but also in the blood. "It's the smoke that goes almost immediately to your bloodstream, which then goes to your head," Lynn said. "You smoke it, it goes into your lungs, into the blood, and for lack of a better term, comes back around and is exhaled in the breath. We're measuring actual THC from the blood stream."

Therefore, the breathalyzer also works with edibles, which affect the bloodstream, and which also usually last longer than smoking. With a handheld device, the breathalyzer isolates THC from the breath via a disposable cartridge. When the analysis is complete, the measurement displays on a screen.


While marijuana breathalyzers may offer more precise measurements, they don't always indicate if a person is "under the influence," said Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws. While the breathalyzer has advantages over urine or blood tests, it provides no definitive evidence that the person is actually impaired. This is especially true given the varying levels of tolerance among medical marijuana patients, daily users, and new users.

Read more: The Confusing Science of Driving While High

"Ultimately, if law enforcement's priority is to better identify drivers who may be under the influence of cannabis, then the appropriate response is to identify and incorporate specific performance measures that accurately distinguish those cannabis-influenced drivers from those who are not," Armentano said, "rather than relying on the detection of compounds that are not consistently associated with behavioral impairment." Some of these other methods include standardized field sobriety tests and performance technology, such as My Canary, an app that tests cognitive impairment.

While this technology is still in its infancy, it's unclear the extent to which law enforcement may utilize it, he said. Hound Labs is planning to have the breathalyzer at commercial capacity by latter half of 2017, Lynn said. The breathalyzer would be available nationally or even internationally.

"When I started this company it was truly to help with this balance of public safety that we need, and also balance that with fairness," Lynn said. "It makes no sense to be arresting people who use cannabis responsibly and are THC positive. That's why we measure THC in the breath."