WHY IT MATTERS: If Texas moves toward a per se THC limit for driving, patients using cannabis for legitimate medical purposes could face DUI charges even when they are not functionally impaired, because THC and its metabolites can persist in blood well beyond any period of active intoxication. CLINICAL OVERVIEW: Cannabis-impaired driving remains a serious public safety challenge because THC affects psychomotor function, reaction time, and divided attention in ways that meaningfully increase crash risk. Unlike alcohol, there is no validated per se blood THC threshold that reliably correlates with functional impairment, making enforcement both scientifically and legally complicated.