Colorado State Troopers perform a road side sobriety test. Photo: Andy Cross / Getty

With states continuing to legalize or decriminalize marijuana, scientists and entrepreneurs are rushing to invent a marijuana breathalyzer that would detect whether someone was impaired while driving, according to STAT, instead of relying on more subjective sobriety tests.

The key problem: While urine and blood tests can show whether someone has used marijuana, they can't test impairment. While some states have set a legal limit of THC for drivers, some experts say that frequent smokers could pass the THC level without actually being impaired, according to STAT.

One new idea: Massachusetts General Hospital researchers are working on a cap, which would use a technique called functional near infrared spectroscopy (fNIRS) to detect changes in blood flow in the brain. The researchers hope to establish patterns in the brain when subjects are high.

Driving high: Many people feel more aware and more capable of driving when stoned than they do when drunk. Dr. Mike Lynn, the CEO and co-founder of Hound Labs, which is working on a marijuana breathalyzer, told STAT that when his lab had people who were high on marijuana drive through an obstacle course, “all of them hit that cyclist when they were stoned, and most of the time, they didn’t even know they’d hit him.”

Go deeper with STAT's full piece.

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