No fixed number of hours after smoking guarantees you are safe to drive after using cannabis. THC affects people differently, and state laws use different standards. Many states use an “effects-based” rule that focuses on proof of actual impairment, while others use “per se” or “zero-tolerance” rules that can make drivers inadmissible to drive based on a THC number alone.
Before you read further, if you have questions about your case, talk with a Pennsylvania DUI attorney at The Law Offices of Steven E. Kellis.
How long after smoking is it safest to wait before driving?
Public safety research suggests a practical window, not a guarantee. After smoking, drivers should wait at least four to six hours before driving. After eating edibles, a longer window of roughly six to eight hours is recommended because effects start later and the presence of THC can last longer. These are general education guidelines, not legal safe harbors.
Can you get a DUI hours or even days after smoking?
Yes, depending on the law and the evidence. THC levels spike in minutes, then fall to low single digits within three to four hours, but frequent users can still show detectable THC a day or more later, even when not impaired.
Some heavy users tested positive after seven days of abstinence from smoking marijuana. A “per se” or “zero-tolerance” state could still charge a driver based on a number, even if the person feels sober, while an effects-based state would focus on signs of actual impairment and the ability to drive.
Per se or zero-tolerance cannabis DUI laws make it illegal to drive with a set THC level in your blood, or with any detectable THC metabolites at all, regardless of whether you’re actually impaired at the time. In contrast, effects-based laws focus on proof of real impairment based on all evidence.
How does law enforcement determine impairment?
In effects-based states, officers and courts look at the full picture. That can include how the person drove, roadside field sobriety test results, a drug recognition expert’s 12-step evaluation, any cannabis odor, and a THC blood test that is weighed with the rest of the evidence. No single test proves impairment by itself in these systems.
Do THC “per se” limits work like alcohol limits?
Not really. Unlike alcohol, no THC number reliably predicts driving impairment across the board. Some states set limits around 5 ng/mL in whole blood, but these thresholds can miss many impaired drivers and also flag unimpaired people who used earlier or were exposed to secondhand smoke.
What is different about edibles compared to smoking?
Edibles take longer to start and can linger. Peak effects can arrive much later than smoking, and drivers may underestimate the timeline. That’s why education campaigns will often recommend a longer wait after ingestion. Mixing cannabis with alcohol or sedating medications raises risk and legal exposure. Since THC and its metabolites can remain detectable on urine tests long after the effects fade, give yourself a longer waiting period before you drive.
Why is working with a DUI attorney helpful in a marijuana DUI case?
Cannabis DUI cases turn on evidence of impairment, not a simple number, and the rules vary by state. An experienced DUI lawyer tests every part of the stop and the investigation, including the reason you were pulled over, the dash or bodycam video, the blood alcohol level, how field sobriety tests were given, and whether a drug recognition expert followed the required steps.
Mr. Kellis brings 25 years of experience in DUI law, National Certification in Field Sobriety Testing, and a background as a former Senior Assistant District Attorney. He understands how these cases are built and how to challenge them.
Who should you call if you are charged with a marijuana DUI?
Deadlines move fast in DUI matters, so getting counsel now can preserve key defenses. We serve clients statewide from six Pennsylvania offices and can begin your defense today. We’ll review your situation, explain your options, and move quickly to protect your license and your case. For a free consultation, call The Law Offices of Steven E. Kellis at (215) 977-4183 today, or contact us online.