Medical Marijuana and Driving in Washington State

Washington State's medical marijuana program gives patients the right to use cannabis legally. It does not protect patients from DUI enforcement. Driving while impaired by cannabis is illegal for everyone — including medical patients — and carries serious legal consequences. Here's what you need to know to stay safe and legal.

Washington's cannabis DUI law

Under RCW 46.61.502, it is illegal to drive while under the influence of cannabis. Washington uses two standards for cannabis DUI:

• Per se limit — a blood THC concentration of 5 nanograms per milliliter (ng/mL) or higher is presumed to indicate impairment. This is similar to the 0.08 BAC limit for alcohol.
• Affected-by standard — even below 5 ng/mL, you can be charged with DUI if a law enforcement officer determines that your ability to drive is "affected" by cannabis. Officers are trained in Drug Recognition Expert (DRE) techniques to detect cannabis impairment.

Medical patient status does not exempt you from DUI law. Having a written authorization or recognition card does not create a legal defense for driving while impaired.

The 5 ng/mL limit and why it's complicated

The 5 ng/mL blood THC limit is controversial among researchers and advocates, because THC blood levels don't correlate well with impairment the way alcohol does. Key issues:

• THC clears blood quickly — peak blood THC occurs immediately after inhalation and drops rapidly. Within 1–3 hours of use, most occasional users drop below 5 ng/mL. However, impairment from THC can persist longer than detectable blood levels.
• Chronic users accumulate THC — regular daily users (many medical patients) can have baseline blood THC above 5 ng/mL even when not recently used and not impaired. This creates a legal gray area for daily medical users.
• Edibles behave differently — THC from edibles peaks in the blood later (1–3 hours after consumption) and at lower concentrations, but impairment can be more pronounced and longer-lasting than inhaled cannabis.

Practical guidance for medical marijuana patients who drive

• Don't drive immediately after use — wait at least 4–6 hours after using cannabis before driving. For edibles, wait longer — the effects can last 6–8 hours or more.
• Know your personal pattern — if you use cannabis medically every day, you may want to discuss your use patterns with your provider. High-frequency users should consider whether their baseline function is impaired.
• Never use in the car — consuming cannabis in a vehicle, even as a passenger, can create additional legal issues
• CBD-only products are safer for driving — non-psychoactive CBD does not cause driving impairment. If you need symptom relief during the day and plan to drive, CBD-dominant products are generally safer.
• Blood tests are the standard — if you're stopped and an officer suspects cannabis impairment, you may be asked to submit to a blood test. Urine tests are not used for roadside DUI enforcement (they detect metabolites, not active THC).

Penalties for cannabis DUI in Washington

A cannabis DUI conviction carries the same penalties as an alcohol DUI:

• First offense: up to 364 days in jail, up to $5,000 fine, 90-day license suspension, mandatory 24-hour minimum jail time or 15 days of electronic home monitoring
• Prior offenses: escalating penalties, including mandatory minimum jail time and extended license revocations
• DUI stays on your driving record and can affect employment, insurance rates, and professional licenses

The bottom line: the legal and safety risks of driving while impaired by cannabis are the same as driving drunk. The medical authorization doesn't change the calculus — plan accordingly.

Get your Washington medical marijuana authorization →