Cannabis & road safety

All forms of cannabis (marijuana) can contain differing levels of mind-altering (psychoactive) drugs. The major psychoactive substance in cannabis is THC (delta-9-tetrahydrocannabinol). Cannabis also contains more than 400 other chemicals.

The THC in cannabis affects many skills required for safe driving, for example:

  • alertness
  • the ability to concentrate
  • coordination
  • reaction time.

These effects can last for many hours after smoking cannabis.

The THC in cannabis can make it difficult to judge distances and react to signals and sounds on the road. Research shows that recent cannabis use increases your crash risk.

When drivers combine cannabis with alcohol, the risk of crashing can be more severe than with either drug alone.

You cannot have any cannabis in your system while driving. There is no safe amount, and each person is affected differently by cannabis use. For information on offences and penalties, see drug-driving penalties and combined drink and drug-driving penalties

Cannabis affects people in different ways

The effects of THC in cannabis depend on factors such as:

  • how much is used
  • the person’s experience with the drug
  • the person’s physical and psychological state, which can be a complex mix of personal factors and environmental factors.
  • how long it has been since the person last used cannabis.

Mixing drugs increases the danger

Using cannabis with other drugs, including alcohol, can reduce your ability to drive safely. A small dose of cannabis can make the effects of a low BAC worse. Some medicines, whether prescribed by a doctor or bought from a supermarket or pharmacy, can also increase the effects of cannabis.

Plan ahead

To reduce the risk of a serious accident, do not use cannabis or other drugs if you are going to drive.

Make alternative arrangements, such as:

  • designate a non-drinking and non-drug taking driver
  • hire a taxi
  • use public transport
  • stay the night (make sure you are not still over the limit in the morning)
  • arrange for someone to pick you up.

Only accept a lift if you are certain the driver has not been drinking or using other drugs.

Was this page helpful?


Take a moment to tell us why. If you'd like a response to your feedback, please message us instead.