Cannabis, Alcohol and Driving: Understanding the Risks

                

Driving requires quick thinking, good judgment, coordination, attention, and fast reaction times. Cannabis and alcohol affect all these abilities. Using cannabis or alcohol before driving increases the risk of a crash. Using cannabis and alcohol together creates even greater impairment and risk.

Driving and cannabis: why it is risky

Many people believe they can drive safely after using cannabis. However, research shows that cannabis affects important skills needed for safe driving. THC, the main psychoactive ingredient in cannabis, can impair:

  • Reaction time
  • Attention and concentration
  • Coordination
  • Decision-making
  • Judgment
  • Ability to respond to unexpected events
  • Perception of time, distance, and speed

These changes can make it harder to react to hazards, stay in a lane, judge distances, or respond quickly to other drivers, pedestrians, cyclists, or changing road conditions.

Mixing cannabis and alcohol: a dangerous combination

Using cannabis and alcohol together is particularly dangerous. Both substances impair driving, but they do so in different ways. When used together, their effects can compound one another, creating greater impairment than either substance alone. Research has shown that combining cannabis and alcohol can significantly worsen driving performance and increase crash risk by up to fortyfold.

How long should you wait before driving?

There is no universal waiting period that guarantees a person is safe to drive after using cannabis. The minimum time someone should wait to drive is 4-6 hours though impairment may last up to 12 hours depending on:

  • THC strength
  • Amount consumed
  • Method of use (smoking, vaping, edible products, beverages)
  • Frequency of use
  • Body size and metabolism
  • Whether alcohol or other drugs were also used

Some effects, including drowsiness and slowed thinking, may last much longer than the feeling of being "high." Edible cannabis products may take longer to begin affecting a person and can impair driving for an extended period.

For this reason, the safest choice is simple: if you have used cannabis, do not drive.

Protect yourself and others

Before using cannabis or alcohol:

  • Plan a safe ride home
  • Use a designated driver
  • Call a taxi or rideshare
  • Use public transportation
  • Stay overnight if necessary

Never get into a vehicle with a driver who has used cannabis, alcohol, or both.

Sources

  • Centers for Disease Control and Prevention (CDC). Cannabis and Driving (2024). [cdc.gov]
  • Government of Canada. Cannabis Impairment (2026). [canada.ca]
  • Government of Canada. Drug-Impaired Driving (2025). [canada.ca]
  • Department of Justice Canada. Impaired Driving Laws and Drug-Impaired Driving FAQs. [justice.gc.ca]
  • National Highway Traffic Safety Administration (NHTSA). Understanding How Marijuana Affects Driving. [nhtsa.gov]
  • NHTSA. Drug-Impaired Driving. [nhtsa.gov]
  • Canadian Centre on Substance Use and Addiction (CCSA). Policy and Regulations: Impaired Driving. [ccsa.ca]
  • Cannabis Evidence. Cannabis and Driving Impairment (evidence review). [cannabisevidence.org]
  • Government of Canada / CAA Road Safety Resources. Cannabis Road Safety Laws. [caa.ca]