Cannabis and driving laws: the short answer
Driving after using cannabis is illegal in all 50 states. Legal status for possession or medical use does not change this. Charges carry state names: DUI, DWI, or OWI.
As of 2025, 24 states and the District of Columbia allow recreational cannabis for adults. Those states wrote the same rule into their statutes: do not drive while impaired by cannabis.
Two ways states prove a cannabis DUI
Impairment laws
Most states charge on observed impairment. An officer records driving behavior, speech, and field sobriety tests. A drug recognition expert may run a 12-step evaluation. The prosecution argues the driver could not operate a vehicle with ordinary care.
Per se laws
Some states set a THC number. If a chemical test meets the number, the charge holds with no proof of bad driving. Colorado, Washington, and Montana use 5 ng/mL of delta-9 THC in whole blood. Nevada uses 2 ng/mL in blood and 5 ng/mL in oral fluid. Pennsylvania uses 5 ng/mL for medical cannabis patients.
Zero tolerance states
A larger group of states uses zero tolerance. Any detectable amount of THC or its metabolites counts as a violation. THC-COOH, a metabolite with no intoxicating effect, can stay in blood and urine for days or weeks after the last use. A person who used cannabis a week ago and is not impaired can still hit that limit.
How police test for cannabis
- Field sobriety tests: horizontal gaze nystagmus, walk and turn, one leg stand.
- Oral fluid swabs: used at roadside in some states.
- Blood draw: the common test for active THC. Some states require a warrant.
- Urine test: detects metabolites, not active THC.
Implied consent laws apply. A driver who refuses a chemical test can lose a license even if the DUI charge fails.
What the research says about THC and driving
Cannabis slows reaction time. It affects lane control and attention. NHTSA states that crash risk rises with THC in the blood. Research has not settled on one blood level that matches impairment for all users. Frequent users carry THC in fat tissue and show high blood levels without matching impairment. Occasional users can show low levels with clear impairment.
CBD, hemp, and drug tests
CBD does not cause a high. Full-spectrum CBD can contain small amounts of THC. Repeated high doses can build up and trigger a positive test for THC or metabolites. Hemp-derived delta-8 THC and delta-9 THC products sold in stores are intoxicating. Driving after those products carries the same legal risk as driving after marijuana.
Penalties
A first cannabis DUI can bring license suspension, fines, probation, and jail time. Some states add mandatory education programs. A commercial driver's license carries stricter rules.
Laws change. Check the state DMV and state code for current numbers and penalties.