美国国家公共电台 NPR The Pot Breathalyzer Is Here. Maybe（在线收听）

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Police across the country are growing concerned about stoned drivers behind the wheel. Thirty states and Washington, D.C., have legalized medical marijuana. Nine of those, plus the District, have legalized recreational pot. One California company now says it's made a major breakthrough in creating what some thought of as a kind of unicorn - a marijuana breathalyzer. NPR's Eric Westervelt has our story.

ERIC WESTERVELT, BYLINE: In his downtown Oakland office, Mike Lynn holds his creation in the palm of his hand. It's a device about the size of a large mobile phone with a small, plastic tube and a slot for a cartridge.

MIKE LYNN: This is a disposable cartridge. And there's a whole bunch of science in this cartridge but...

WESTERVELT: Lynn is not some pipe dream stoner inventor. The entrepreneur is also a practicing E.R. trauma doctor and an active SWAT team medic. He's seen firsthand the sometimes devastating impact of drunk and drugged drivers. The CEO of Hound Labs, the scientific device company he founded, slips a new cartridge into the pot breathalyzer and starts to blow.

LYNN: All right. Here we go.

WESTERVELT: Indicator bars show whether the machine detects any THC, the psychoactive component in pot. Tools now on the market to determine marijuana use test blood, saliva or urine. But those devices can take days for a result. And they can't tell whether a person has smoked a half hour ago or eight days ago. THC dissolves in fat, so it can stay in your body up to a month after use. But Dr. Lynn says his company's device detects whether someone has smoked pot in the last two hours, what's considered the peak impairment window. It accurately does that, he says, by measuring the mere presence of THC molecules in parts per trillion in your breath.

LYNN: And that's in contrast to alcohol, which is parts per thousand. THC is something like a billion times less concentrated than alcohol. That's why it hasn't been done before because it really is hard.

WESTERVELT: The company hopes to have the breathalyzer ready for sale by early next year. A handful of police departments, including Boston, plan to work with Hound Labs to test the device starting this fall.

LYNN: For law enforcement, their issue is trying to figure out who's potentially impaired versus, hey, who's somebody who smoked maybe yesterday and is not impaired. They're interested in it providing objective data for them at the roadside.

WESTERVELT: Just like they have for alcohol. But a big problem - there's still no scientific or legal consensus on what amount of THC equals functional impairment. That matters to the courts. Only seven states have set basic legal guidelines as to how much THC in the system makes you dangerous behind the wheel.

At Harvest, a stylish dispensary in San Francisco's Mission District, David Downs does some market research.

DAVID DOWNS: Romo (ph), which is really scrumptious.

WESTERVELT: The California bureau chief for the cannabis news site Leafly has his nose in a jar of Indica-dominant hybrid buds.

DOWNS: Very, very complex - it has notes of purple and grape underneath it and pepper. And it can be very multi-dimensional. And so...

WESTERVELT: Downs, an expert who's written four books on marijuana, says many in the industry would like to see more states where pot is legal try to settle on a science-based cut-off limit for THC level impairment.

DOWNS: That would eliminate a major roadblock to, like, further acceptance and normalization and sort of mainstreaming of cannabis as a consumer product. By far, the biggest criticism that's raised as these reform efforts advance is the issue around driving.

WESTERVELT: Studies since legalization on marijuana and driving have been mixed. One at Columbia University showed that half of young drivers age 16 to 25 who died in car crashes were under the influence of alcohol, marijuana or both. But exactly what role THC played in those crashes is unclear, says epidemiologist Guohua Li, who conducted that study.

GUOHUA LI: We need more research to establish the dose-response relationship between THC level and crash risk.

WESTERVELT: Another study by the National Highway Traffic Safety Administration showed that while marijuana users are more likely to be involved in crashes, that risk may be in part because pot users are also more likely to be young men - a group already at high risk for car wrecks. Eric Westervelt, NPR News, San Francisco.