How Long After Smoking Can I Drive? Wait Times and DUI Limits

Wait at least five hours after smoking or vaping cannabis before you drive, and treat that as a floor rather than a promise. That number comes from a meta-analysis of 155 experimental studies looking at when driving-related skills return to baseline for an average person using a typical dose.¹ Higher-potency products, larger doses, edibles, and individual differences in metabolism can push impairment well past that window. And in most states, being legally in the clear to drive is a separate question from being safe to drive, because the law can catch you even after the impairment has faded.

Why Five Hours, and Why It’s Only a Minimum

THC slows your reaction time, distorts your sense of distance, and weakens the divided attention that driving demands: scanning mirrors, tracking speed, reading signs, anticipating what other drivers will do.² Research consistently shows that cannabis increases lane weaving and slows response to unexpected hazards.¹

Here’s the part that trips people up. The subjective feeling of being high fades before the actual impairment does. You can feel fine to drive while your reaction time and lane-tracking are still measurably worse than normal. That mismatch is why “I feel sober” is a bad test, and why the five-hour figure from controlled research is a better starting point than what your body is telling you at hour three.

Edibles Need a Longer Wait

The five-hour figure applies to smoking or vaping, where impairment starts within minutes and is measurable within the first hour. Edibles work differently. THC that has to pass through the digestive system peaks later and clears more slowly. In one study, participants who consumed cannabis edibles reported altered subjective effects for seven hours and were less willing or able to drive for up to six hours.³

A more cautious wait for edibles is six to eight hours, and even that can fall short for high-dose products. Because the onset is slower and less predictable, it’s harder to know exactly when you peaked, which makes it harder to know when you’ve come down.

What Can Stretch Your Personal Wait Time

The five-hour guideline is an average. Several things push your own timeline longer:

Potency. A concentrate at 80% THC produces stronger and longer-lasting impairment than a joint at 15%.
Dose. More consumed in a session means a longer clearance.
Frequency of use. Daily users develop some tolerance, but research has not shown that tolerance eliminates driving impairment. One study found that daily users who had abstained for at least eight hours still had baseline blood THC levels averaging 5.0 ng/mL before smoking anything during the session. That’s a problem, because some states treat 5 ng/mL as the threshold for presumed impairment.⁴
Body composition. THC is fat-soluble and gets stored in fat tissue, so people with higher body fat percentages may retain it longer, though the link between stored THC and active impairment is complicated.
Individual metabolism. How quickly your liver processes THC varies. Two people sharing the same joint at the same time will not necessarily be impaired for the same duration.

The Legal Wait Isn’t the Same as the Safe Wait

Even after impairment has cleared, you may not be legally clear. There is no single national standard for cannabis-impaired driving, and states take three different approaches.

Impairment-Based Laws

Most states require prosecutors to prove you were actually impaired. Evidence comes from the officer’s observations of your driving, field sobriety tests, and, in some cases, evaluations by a drug recognition expert. The focus is on how you were driving, not on a number from a blood test.

Per Se THC Limits

Some states set a specific blood THC concentration that creates a legal presumption of impairment, similar to the 0.08% alcohol standard. These per se limits range from 2 to 5 nanograms of THC per milliliter of blood.⁵ If your blood THC meets or exceeds the threshold, the state does not have to prove impairment any other way. Frequent users are most exposed here, because residual THC can sit in blood after the high is long gone.

Zero-Tolerance Laws

About a dozen states make it illegal to drive with any detectable THC or its metabolites in your system. Whether you were actually impaired doesn’t matter. A positive test is enough. Because metabolites can linger for days or weeks after use, zero-tolerance rules can reach drivers who consumed cannabis long before the stop and were completely sober at the wheel.

A Drug Test Can Detect THC Long After You’re Safe to Drive

This is the point that catches people off guard. Detection windows are not impairment windows, and in per se and zero-tolerance states, a positive test alone can produce a DUI charge.

Blood: generally detectable for up to 12 hours after a single smoking session; longer for frequent users because THC releases slowly from fat tissue.
Oral fluid (saliva): up to 24 hours after use. Some jurisdictions are moving toward roadside oral fluid testing as a screening tool.⁶
Urine: 1 to 30 days depending on frequency. A casual user might clear in under two weeks; a daily user can test positive for four weeks or longer.⁶
Hair: roughly three months, mainly as a qualitative indicator of heavy use during that window. Hair testing is more common in employment screening than in DUI enforcement.⁷

Practically, this means your body may still contain enough THC to trigger a violation in some states well after your impairment has cleared. A medical marijuana card doesn’t change this in most contexts; in impairment-based states it can help explain a positive result, but it isn’t a defense if the state proves you were actually impaired, and in zero-tolerance and per se states it may offer little or no protection at all depending on where you are.

If You’ve Also Had Alcohol, Don’t Drive

Combining cannabis and alcohol is far more dangerous than either alone. The two produce a synergistic effect on impairment, meaning the combined impact is greater than the sum of the parts.⁸ The crash data is stark. One study of fatally injured drivers found that those positive for marijuana alone had about 1.5 times the odds of a fatal crash compared to sober drivers. Drivers positive for both alcohol and marijuana had over 25 times the odds.⁹ The five-hour rule does not apply once alcohol is in the mix. Don’t drive.

Commercial Drivers: No Wait Is Long Enough

If you hold a commercial driver’s license, federal rules override any state legalization. The Department of Transportation prohibits marijuana use for anyone in a safety-sensitive transportation role, regardless of what your state allows.¹⁰

CDL holders face DOT drug testing before employment, at random, after accidents, and on reasonable suspicion. Marijuana is on the panel. A positive result or a refusal triggers immediate removal from safety-sensitive duties, and the violation goes into the FMCSA Drug and Alcohol Clearinghouse. As of late 2024, state licensing agencies must downgrade or remove commercial driving privileges until the driver completes the full return-to-duty process, which requires evaluation by a qualified substance abuse professional, any recommended education or treatment, and a negative return-to-duty test, followed by continued follow-up testing.¹¹ For a CDL holder, there is no “wait a few hours” version of the answer.

A Simple Plan

Wait at least five hours after smoking or vaping, and treat that as a minimum rather than a guarantee. Wait six to eight hours after an edible, and longer for high-dose products.¹³ If you also drank, don’t drive at all. And plan your ride before you consume, the same way you would before a night of drinking, because impairment outlasts the subjective high and the legal consequences of getting the timing wrong can follow you for years.

1
National Center for Biotechnology Information (NCBI). Recent Advances in the Science of Cannabis-Impaired Driving
2
Centers for Disease Control and Prevention. Cannabis and Driving
3
National Center for Biotechnology Information (NCBI). The Effect of Cannabis Edibles on Driving and Blood THC
4
National Center for Biotechnology Information (NCBI). Simulated Driving Performance Among Daily and Occasional Cannabis Users
5
National Conference of State Legislatures. Drugged Driving – Marijuana-Impaired Driving
6
National Center for Biotechnology Information (NCBI). Objective Testing – Urine and Other Drug Tests
7
National Center for Biotechnology Information (NCBI). Comparison of Cannabinoids in Hair With Self-Reported Cannabis Consumption in Heavy, Light and Non-Cannabis Users
8
PMC (PubMed Central). Simultaneous Alcohol/Cannabis Use and Driving Under the Influence in the U.S.
9
Centers for Disease Control and Prevention. Interaction of Marijuana and Alcohol on Fatal Motor Vehicle Crash Risk
10
Federal Motor Carrier Safety Administration. A CDL Driver Tests Positive, or Refuses to Take, a DOT Drug or Alcohol Test
11
Federal Motor Carrier Safety Administration. Drug and Alcohol Clearinghouse – FAQ Topics