Drugs and Driving > Alcohol & other drugs > Cannabis
Alcohol & other drugs: Cannabis
Research indicates that drivers who have recently used cannabis are at a similar level of risk of having a car accident as a driver with a blood alcohol concentration (BAC) above 0.051.
Effects of cannabis on driving
Cannabis is a depressant drug that may also have some hallucinogenic effects. The depressant effects slow down the activity of the brain and other parts of the central nervous system while the hallucinogenic effects can distort a person’s perception of the world, or result in people seeing or hearing things that don’t exist.
The effects of cannabis can be different for each person and are influenced by a range of factors such as:
-
How much is used. Larger amounts can produce different effects.
-
How much THC (delta-9 tetrahydrocannabinol), the active ingredient, it contains.
-
How it is used. For example, when cannabis is smoked the effects are experienced very quickly and may last up to 5 hours. When cannabis is eaten, the onset of effects can be delayed by about 60–90 minutes and can last up to 24 hours.
-
The psychological and physical attributes of the person using it. Factors such as a person’s mental or emotional state, and physical health, can influence the effects of a drug.
This makes it difficult to predict exactly, in what way, and for how long, cannabis will affect a person’s ability to drive safely. As a general guide, some of the effects of cannabis that can affect a person’s driving ability include:
-
reduced coordination and slower reaction times
-
slower information processing ability, confusion and impaired thinking
-
changes in visual, auditory, time and space perception.
The “hangover” effects of cannabis, which can last for several hours, can also impair a person’s driving ability.
A person who has used cannabis may think that they can alter their driving to counteract any impairment to their driving ability, however, the effects of cannabis may mean that the driver has an altered view and experience of reality. This means that their actions and responses may be quite different to what is actually needed, and they may be unaware how much their driving skills are affected after using cannabis.
As a rough guide, the devices used in Victoria’s random roadside saliva testing can detect the THC (Delta-9 tetrahydrocannabinol) in cannabis for several hours after the last use.
Safer driving tips
If you intend to use cannabis, the safest option is not to drive. Especially avoid driving late at night or early in the morning when natural tiredness may increase the sedating effects of cannabis.
1 Arrive Alive 2008 "Random roadside drug testing" (accessed 19 February 2008)
DDSN Interactive.