A federal traffic safety agency says that there’s “relatively little research” backing the idea that THC concentration in the blood can be used to determine impairment, calling into question laws in several states that set “per se” limits for cannabinoid metabolites. In a draft report posted last month, the National Highway Traffic Safety Administration (NHTSA) … Continue reading Federal Agency Says There’s ‘Little Research’ Supporting Marijuana Driving Impairment Tests Based On THC Concentration