What are the legal limits for marijuana in Washington?
Washington legalized recreational marijuana in 2012, but driving under the influence of cannabis remains a criminal offense. The state enforces strict limits on THC levels for drivers, with zero tolerance for minors and clear penalties for impairment.
Alcohol Limits for Comparison
For adults 21 and older, the legal blood alcohol concentration (BAC) limit is 0.08%. For anyone under 21, Washington enforces a limit of 0.02% within 2 hours of driving. An alcohol level of 0.02% or higher, or any detectable amount of THC, can lead to penalties and a Minor DUI charge.
THC Limits for Adults
Washington law sets a measurable limit for marijuana impairment. If a driver’s blood contains 5 nanograms per milliliter (ng/mL) or more of active THC within two hours of driving, it counts as a per se DUI—prosecutors don’t need additional proof of impairment.
However, even with less than 5 ng/mL, a driver can still be charged if there’s evidence of impairment, such as unsafe driving or failing field sobriety tests. The THC limit acts as a benchmark, not a guarantee of safety.
Zero Tolerance for Minors
Drivers under 21 are treated differently. Any detectable THC in a minor’s blood can result in a DUI charge. There’s no threshold to fall below—any amount can trigger criminal penalties, license suspension, and higher insurance rates. The goal is to discourage all cannabis use among underage drivers.
Medical Marijuana and Driving
Having a medical marijuana authorization card does not exempt anyone from DUI laws. Patients can legally possess more cannabis but are still prohibited from driving impaired. A registered medical user with 5 ng/mL or more of THC—or who shows visible signs of impairment—can still be charged with DUI.
How Long Should You Wait Before Driving?
There’s no defined waiting period under Washington law. THC affects everyone differently depending on tolerance, dosage, and method of use. Occasional users might fall below 5 ng/mL after a few hours, while frequent users could test above the limit even when they don’t feel high. Because of that variability, it’s safest to wait several hours or longer before driving.
Key Takeaways
- Adults: Legal limit is 5 ng/mL of active THC.
- Minors: Zero tolerance—any amount of THC can result in DUI.
- Medical cardholders: Not exempt from DUI laws.
- No fixed waiting time—effects and THC levels vary widely.