On your mark. Get set. Blow: The race to build a breathalyzer for weed

Old tests for marijuana looked for trace elements in things like blood, urine, and hair. But legalization changed all of this. Suddenly marijuana testing became a spectrum, with the need to delineate between the person who threw five on it a week ago, but who still has evidence of weed in their bodily fluids, and the person who’s dangerously blazed right this moment. 

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