Legalizing marijuana in Washington didn’t change one thing: driving under its influence is still a crime. I’ve watched clients come into my office genuinely surprised they’re facing a DUI charge after using cannabis legally at home hours before getting behind the wheel. That surprise is understandable, but it doesn’t slow the criminal process. Understanding exactly how the law is written and where it creates real exposure is the first step toward knowing what your options actually are.
I’m Attorney Matthew T. Hale, and I’ve been defending clients in Seattle courts for over 27 years. Marijuana DUI cases have become a significant part of my criminal defense practice, and they present challenges that are fundamentally different from alcohol DUI cases. The science is contested, the testing process can catch defendants off guard months after an arrest, and the law is written in ways most people don’t fully understand until they’re already charged.
How Washington’s Marijuana DUI Law Actually Works
RCW 46.61.502 creates two independent paths to conviction, and most people only know about one of them. The first is a per se standard: if a blood test shows a THC concentration at or above 5 nanograms per milliliter within two hours of driving, the law treats that as DUI regardless of whether you were actually impaired. The second path doesn’t require any THC measurement at all. A prosecutor can pursue a conviction based on evidence of actual impairment even if your blood test came back below the limit or wasn’t taken at all.
That two-track structure matters because it closes off what seems like an obvious defense. Being below 5 ng/mL doesn’t mean you’re safe. And being above it doesn’t automatically mean you’ll be convicted, because the per se limit has its own vulnerabilities that can be challenged at trial.
The Washington Supreme Court addressed the constitutionality of the 5 ng/mL standard directly in State v. Fraser in May 2022, upholding it and confirming it won’t be struck down as arbitrary. That ruling shapes defense strategy: arguments against the limit’s scientific validity remain available at trial, but the constitutional challenge is settled. One more thing worth knowing: RCW 46.61.502(2) explicitly states that authorization to use marijuana under Washington law is not a defense. Your prescription or recreational purchase receipt has no bearing on a DUI charge.
Why THC Testing Creates Problems a Breathalyzer Doesn’t
Alcohol and THC don’t behave the same way in the body, and the testing process reflects that difference in ways that create real complications for defendants. When an officer suspects alcohol impairment, a roadside breath test produces a result within minutes. THC requires a blood draw, and under Washington’s implied consent law, officers typically need a warrant before drawing blood. That process takes time. The blood sample then goes to a state lab, and backlogs mean results can take months. I’ve had clients call me six months to a year after an arrest when charges finally came through, because they assumed no charges were coming. That assumption is a dangerous one.
THC is fat-soluble, which means it binds to fatty tissue and can remain detectable in the bloodstream for days or even weeks after any impairing effects have worn off. A regular cannabis user can test well above 5 ng/mL while being entirely sober by any functional measure. That gap between a blood number and actual impairment at the time of driving is one of the most significant vulnerabilities in these cases, and it’s where a careful defense can do real work.
What Happens After a Marijuana DUI Arrest in Seattle
A marijuana DUI arrest triggers two separate processes simultaneously, and most people focus entirely on the criminal case while missing a critical administrative deadline.
The DOL Hearing Deadline
The Washington Department of Licensing will administratively suspend your license 30 days after your arrest unless you request a hearing. That request must be made within 7 days of the date of arrest or the date notice was given. Some sources still cite 20 days, but that figure reflects the pre-2019 rule. The official DOL form and the statute as amended effective January 1, 2019 confirm the 7-day deadline. Missing it means the suspension becomes automatic, and there’s no appeal of a deadline you’ve already missed.
Where Your Case Is Heard
If you were arrested within Seattle city limits, your arraignment will be held at Seattle Municipal Court. Arrests in unincorporated King County proceed to King County District Court. The venue matters because local court practices, prosecutors, and procedural norms vary. Knowing the specific courtroom you’re walking into is part of building a realistic defense strategy.
Bail Conditions
Marijuana DUI defendants often face higher bail conditions than alcohol DUI defendants. The reason is practical: electronic home monitoring and ignition interlock devices are designed to detect alcohol, not cannabis. Because courts can’t impose those standard monitoring tools to ensure compliance, they may require higher monetary bail or more restrictive conditions to manage the perceived risk.
Penalties & What a Conviction Means Long-Term
A first-offense marijuana DUI is charged as a gross misdemeanor under RCW 46.61.5055. The penalties are significant: up to 364 days in jail, a fine of up to $5,000, a minimum 90-day license suspension, and at least one year of an ignition interlock device requirement after your license is restored. Actual sentencing depends on the facts of the case and your prior record.
A DUI conviction in Washington is permanent. There’s no expungement available. The conviction stays on your record, and the collateral consequences reach into employment, professional licensing, housing applications, and immigration status. For non-citizens, a DUI conviction can trigger serious immigration consequences depending on visa status and the specific charges involved.
If you have three or more qualifying prior offenses within 15 years, or a prior conviction for vehicular homicide or vehicular assault under the influence, the charge can be elevated to a felony. That threshold is a reason to take even a first offense seriously rather than treating it as a routine matter.
Where a Marijuana DUI Defense Can Actually Win
A marijuana DUI charge isn’t a foregone conclusion. There are several points in these cases where the evidence is genuinely vulnerable, and building an effective defense means identifying which of those vulnerabilities applies to your specific arrest.
The Traffic Stop
Every piece of evidence in a DUI case flows from the initial traffic stop. If law enforcement didn’t have reasonable suspicion to pull you over, the stop itself may be unlawful. Under the Fourth Amendment and Washington state law, evidence gathered following an unlawful stop (including blood test results) can be suppressed. A successful suppression motion on the stop can effectively end the case.
Blood Test Reliability
Even when the stop is valid, the blood evidence itself can be challenged. RCW 46.61.506 governs the admissibility of blood test results, setting requirements for how samples must be collected, analyzed, and handled. Chain of custody, the timing of the draw relative to when you were driving, lab procedures, and the fundamental disconnect between a static THC concentration and actual impairment at the wheel are all areas where a thorough review of the state’s evidence can reveal weaknesses.
DRE Evaluation Validity
In many marijuana DUI arrests, the officer calls in a Drug Recognition Expert, or DRE. This is a law enforcement officer trained in a 12-step evaluation protocol designed to identify drug impairment. The problem is that the field sobriety tests embedded in that protocol were developed and validated for alcohol, not cannabis. The scientific reliability of DRE evaluations for detecting marijuana impairment is genuinely contested, and that contested status creates room to challenge the DRE’s conclusions at trial.
What to Do If You’re Facing a Marijuana DUI in Seattle
The 7-day DOL deadline runs whether or not you’ve hired an attorney. So does the clock on preserving evidence while the details of the stop and arrest are still fresh. Waiting to see if charges materialize is a risk. Lab delays mean charges can surface months after the arrest, when documents and memories have faded. The science around the 5 ng/mL limit is contested, the testing process has documented vulnerabilities, and the law, while strict, doesn’t eliminate the ability to mount a serious defense. If you’re facing a marijuana DUI charge, reach out to Hale Law Enterprises at (206) 207-4776 for a free initial consultation. I handle every case personally and am available around the clock.