Per se

A "per se" standard, in the impaired-driving context, makes it unlawful to operate a vehicle with a controlled substance or metabolite in the body at or above a specified concentration, regardless of whether the driver is actually impaired. Per se laws remove the prosecution's burden of proving impairment in fact. For cannabis, per se THC thresholds vary sharply by state: Illinois, Washington, and Montana use 5 ng/mL whole blood; Nevada and Ohio use 2 ng/mL (Ohio is considering raising to 5 ng/mL under SB 55); Pennsylvania applies a strict 1 ng/mL threshold; Colorado uses a 5 ng/mL rebuttable "permissible inference" rather than strict per se liability (C.R.S. § 42-4-1301(6)(a)(IV)). Zero-tolerance states (Arizona, Georgia, Indiana, Iowa, Oklahoma, Rhode Island, South Dakota, Utah, Wisconsin) criminalize any detectable THC or metabolite, subject to medical-patient exceptions in some. The scientific validity of per se THC thresholds is widely criticized because THC pharmacokinetics do not track impairment the way blood alcohol concentration tracks alcohol impairment. *→ See also: DUI, DWI, Implied consent