THE CANNABIS LIE is a reporting series examining how cannabis policy turns shaky assumptions into hard penalties. In THE CANNABIS LIE: Vol. 2, The Fiction of Impairment, THC detection is often treated like proof of impairment, even though blood levels show a weak, inconsistent relationship to functional driving ability. This installment explains why per se THC limits and zero tolerance rules create false certainty, why urine metabolites only show prior exposure, and why real impairment should be demonstrated through behavior and context, not presumed from a lab result.