How Long After Smoking Weed Can You Get a DUI?

Marijuana impairment from smoking or vaping typically fades within five to seven hours, and clinical guidelines suggest waiting at least six to eight hours before driving. But how long after smoking weed you can get a DUI is a much longer window than how long you actually feel high. Depending on your state’s law and the type of test used, you can be arrested and convicted days or even weeks after your last use. About a dozen states make it illegal to drive with any detectable trace of THC or its metabolites in your body, and those metabolites can linger for a month in regular users.¹

How Long the Impairment Itself Lasts

THC affects the brain regions that control coordination, reaction time, judgment, and spatial awareness. The subjective high fades faster than the measurable driving impairment does, which is where a lot of drivers get into trouble.

A systematic review of controlled studies found that most driving-related cognitive skills recover within about five hours of inhaling 20 mg of THC, with nearly all skills back to baseline within seven hours.² Edibles are slower and longer. Because THC absorbs through the digestive system, impairment from an edible can last eight to twelve hours. Clinical guidelines recommend waiting at least six to eight hours after inhaling and eight to twelve hours after eating an edible before driving.³

Those numbers assume a moderate dose. High-potency products, larger amounts, or infrequent use all push impairment further out. If you consumed a concentrate or a high-dose edible, the conservative end of those ranges is not conservative enough.

How Long THC Stays Detectable

Impairment is one clock. Detection is another, and it runs much longer. The window depends on the test:

Blood: Active THC in blood drops roughly 90 percent within the first hour after smoking, but it can remain detectable for up to about 12 hours in occasional users. Frequent users are a different case entirely. THC is fat-soluble and leaches slowly back into the bloodstream, so regular users can have baseline blood THC above 5 ng/mL even when they are not impaired at all.⁴
Saliva: Oral fluid tests pick up THC for about 24 to 72 hours, with heavier users at the longer end.
Urine: Urine tests detect THC-COOH, an inactive metabolite unrelated to impairment. A single use might show for about three days. Daily use can produce positive results for 30 days or more.
Hair: Hair follicle tests can detect THC metabolites for up to 90 days, though these are rarely used in DUI cases.

A positive test does not prove you were impaired when you were driving. It proves cannabis was in your body at some point. In many states, that alone is enough for a conviction.

Why Your State’s Law Decides Your Real Risk

Unlike alcohol, where 0.08 percent BAC reliably indicates impairment, no THC blood level works the same way. Researchers in the largest randomized, double-blind, placebo-controlled trial on the question concluded that THC concentrations in blood “cannot be used as a sole indicator of impairment.”⁴ The law has not caught up to that finding, and states have taken very different approaches. Which category your state falls into is what determines how long after use you remain legally exposed.

Per Se Laws

Five states set a specific THC blood concentration as the legal limit: Illinois, Montana, Nevada, Ohio, and Washington. Exceed the limit and you are guilty regardless of whether you showed any signs of impairment. Thresholds range from 2 ng/mL to 5 ng/mL.¹ Washington sets the limit at 5 ng/mL within two hours of driving.⁵ For frequent users whose baseline levels sit near or above the threshold, the window of legal exposure can extend well past any actual impairment.

Zero-Tolerance Laws

Twelve states prohibit driving with any detectable amount of THC or its metabolites in your system: Arizona, Delaware, Georgia, Indiana, Iowa, Michigan, Oklahoma, Pennsylvania, Rhode Island, South Dakota, Utah, and Wisconsin.¹ In these states, a urine test showing inactive metabolites from cannabis used two weeks ago can support a DUI conviction. For regular cannabis users in a zero-tolerance state, you are effectively never in the clear.

Permissible Inference Laws

Colorado uses a permissible inference approach: if your blood THC is 5 ng/mL or higher, the jury is allowed to infer you were impaired, but you can fight the inference by showing you were not actually impaired.¹ Overcoming it in practice is difficult, but the defense at least exists on paper.

Impairment-Based Laws

The remaining states require the prosecution to prove you were actually too impaired to drive safely. Evidence typically combines the officer’s observations, field sobriety test performance, Drug Recognition Expert evaluations, and chemical test results. These cases are harder for prosecutors to win, which narrows your realistic legal exposure to something closer to the actual impairment window.

Why Blood THC Behaves Nothing Like Alcohol

The reason the legal window stretches so far past the impairment window comes down to how THC is stored. It is fat-soluble, so it gets stored in body fat and releases slowly over time. A daily user can walk into a traffic stop with blood THC above 5 ng/mL without having consumed anything that day and without being impaired. Meanwhile, an occasional user who smoked an hour ago might have a lower blood level but noticeably worse driving. The test result and the actual risk you pose behind the wheel are only loosely connected, but the law often treats the number as if it were definitive.

There is also a delay problem. Blood THC drops steeply between the traffic stop and the eventual blood draw at a hospital or station.⁴ A reading of 3 ng/mL at the hospital might have been much higher at the moment you were pulled over. In some states, prosecutors argue backward from the delayed result; in others, the delayed number is what the court works with.

Mixing Marijuana and Alcohol

Combining cannabis and alcohol is one of the most common ways people end up with a DUI they did not expect. Together, the two substances produce worse coordination, slower reaction times, and more distorted perception of speed and distance than either does alone.

Legally, the combination creates extra exposure. If your blood alcohol is under 0.08 and your THC is under the per se limit, you might assume you are fine. You are not. Prosecutors can and do argue that two substances, each below its individual threshold, added up to impairment. Several states have combination-specific provisions written for exactly this scenario. Being a little high and a little buzzed is a common path to a charge.

If You Refuse the Chemical Test

Every state has an implied consent law. By holding a driver’s license and using public roads, you have already agreed to submit to chemical testing if lawfully arrested for impaired driving.⁶ For marijuana cases, that typically means a blood test, since there is no validated breath test for THC.

Refusing does not make the problem go away. In most states, refusal triggers an automatic administrative license suspension separate from any criminal DUI penalty, and many states impose harsher suspensions for refusal than for a failed test. The refusal itself can also be introduced at trial, where prosecutors will argue you refused because you knew you would fail. Whether refusing is a rational gamble depends heavily on your state and what evidence the officer already has.

How Long You Should Actually Wait

The honest answer depends on whether you are asking about safety or legal risk, because they are two different clocks.

For safety, the research points to a minimum of six to eight hours after smoking or vaping, and eight to twelve hours after eating an edible.³ Higher doses, stronger products, and lower tolerance push those numbers up.

For legal risk, the timeline stretches much further. In a zero-tolerance state, regular cannabis users can test positive for THC metabolites weeks after their last session. In a per se state, frequent users can carry baseline blood THC levels above the legal limit even when completely sober. The only way to guarantee you will not test positive is to stop using cannabis long enough for your body to clear it fully, which can take 30 days or more for daily users.

That gap between no longer impaired and no longer legally exposed is the space where most marijuana DUI arrests happen. Before you drive, find out which category of law your state uses. In an impairment-based state, waiting out the safety window is a reasonable plan. In a per se or zero-tolerance state, if you use cannabis regularly, driving carries a legal risk that has almost nothing to do with how you feel.

1
National Conference of State Legislatures. Drugged Driving Marijuana-Impaired Driving
2
ScienceDirect. Determining the Magnitude and Duration of Acute THC-Induced Driving and Cognitive Impairment: A Systematic and Meta-Analytic Review
3
International Centre for Cannabis Evidence. Cannabis and Driving Impairment
4
PubMed Central. Driving Under the Influence of Cannabis: Impact of Combining Toxicology Testing With Field Sobriety Tests
5
Washington State Legislature. RCW 46.61.502 Driving Under the Influence
6
National Highway Traffic Safety Administration. BAC Test Refusal Penalties