IL SB1889

Amends the Illinois Vehicle Code to specify that DUI violations based on THC concentration must measure "free tetrahydrocannabinol" (parent delta-9-THC) rather than total THC metabolites

Establishes legal THC limits of 5 nanograms or more per milliliter in whole blood, or 10 nanograms or more per milliliter in other bodily substances (excluding urine), within 2 hours of driving

Defines "free tetrahydrocannabinol concentration" as the amount of parent delta-9-tetrahydrocannabinol detected in blood or another bodily substance, excluding urine

Creates a presumption of cannabis impairment when drivers meet or exceed the specified THC thresholds, while concentrations below those levels may still be considered with other evidence

Maintains exemption for medical cannabis patients with valid registry cards under the Compassionate Use of Medical Cannabis Program Act, unless impairment is demonstrated