All forms of cannabis can contain different levels of mind-altering (psychoactive) drugs; the major substance being THC (delta-9-tetrahydrocannabinol), the main active chemical in cannabis (marijuana). They also contain more than 400 other chemicals.

The THC in cannabis (marijuana) affects many skills required for safe driving:
alertness, the ability to concentrate, coordination, and reaction time. These effects can last up to 24 hours after smoking cannabis (marijuana). The THC in cannabis (marijuana) use can make it difficult to judge distances and react to signals and sounds on the road.

Recent use of THC greatly increases accident risk.

Research shows that after recent use of THC the risk of being killed in a fatal crash is similar to a driver with a BAC of up to approximately 0.15.

When users combine cannabis (marijuana) with alcohol the hazards of driving can be much more severe than with either drug alone

It is illegal to drive while affected by cannabis. There is no safe amount. For information on offences and penalties, see: Drugs and Driving.

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 its been since the person last used cannabis

Mixing drugs increases the danger
Using cannabis with other drugs, including alcohol, can markedly reduce your ability to drive safely. A small dose of cannabis can make the effects of a low BAC much 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 arrangement, 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.