How Long After Smoking Cannabis Can You Drive?

Driving under the influence of cannabis is illegal and dangerous. In the UK, the law is strict: even trace amounts of THC (tetrahydrocannabinol) in your system can lead to a drug-driving conviction.

But how long should you wait before getting behind the wheel after smoking weed? The answer depends on several factors—including how much you used, how often, and how your body processes THC.

What Does UK Law Say?

Under UK law, driving with cannabis in your system is illegal if you're over the specified legal limit, regardless of whether you're impaired or not. THC (the active ingredient in cannabis) has a legal limit of 2 micrograms per litre of blood—an extremely low threshold.

This limit is so strict that even if you don’t feel high anymore, you could still test positive and be charged.

So How Long Should You Wait After Smoking Cannabis?

There’s no one-size-fits-all answer, but here’s a general guide based on how your body processes THC:

User Type	Wait Time Before Driving (Estimate)
Occasional (1x/week)	6–12 hours
Moderate (few times/week)	12–24 hours
Daily/Heavy User	24–48+ hours

These are conservative estimates. THC can be detectable in your blood for over 24 hours, and in urine for days or even weeks in heavy users.

How Long Does THC Stay in Your System?

Blood: Detectable for 6 to 24+ hours
Saliva: 12 to 24 hours
Urine: Up to 30 days (especially in regular users)

Importantly, you can still test positive even if you no longer feel impaired. That’s why UK law focuses on presence, not intoxication.

Penalties for Drug Driving in the UK

Getting caught driving with cannabis in your system comes with severe penalties:

Minimum 1-year driving ban
Unlimited fine
Up to 6 months in prison
Criminal record
Licence endorsement for 11 years

It can also impact your job, insurance costs, and ability to travel internationally.

Final Advice: When Is It Safe to Drive?

To stay within the law and protect yourself and others:

Avoid driving for at least 24 hours after using cannabis—especially if you're a regular user.
Don’t rely on how you feel. Even if you’re no longer “high,” you could still fail a drug test.
Never mix cannabis with alcohol and drive—this increases impairment and legal risk.

If you're using medical cannabis legally, you still must not drive if impaired, and must carry documentation confirming your prescription.

Summary

Cannabis Use	Legal to Drive After?
Recreational (within 24h)	❌ No – risk of testing positive
Medicinal (impaired)	❌ No – still illegal if impaired
24+ hours after single-use	✅ Safer – but not guaranteed

Final Word

In the UK, drug-driving laws around cannabis are strict and unforgiving. With such low thresholds for THC, even casual use can land you in serious legal trouble if you drive too soon. The safest rule is simple: don’t drive for at least 24 hours after cannabis use—and longer if you're a regular user.