Drugs and driving laws

In the last five years, around 41 percent of all driver and motorcyclist fatalities who were tested had drugs in their system.

Drivers who take drugs are much more likely to be involved in a crash than drug-free drivers, and are often responsible for these crashes.

Drug driving laws and road safety

It’s illegal to drive, attempt to drive or supervise a learner while affected by drugs. You cannot drive while impaired by any drug.

Drivers face harsh penalties if they are caught driving with drugs in their system. These laws apply if you are on a private property or public road. 

How drugs affect driving ability

Drugs affect you in different ways:

• depressants such as cannabis impair brain function, attention and concentration
• stimulants such as ice, speed and ecstasy affect coordination, distance judgements and risk assessment
• when illicit drugs wear off, you can be excessively sleepy and distracted
• using multiple drugs makes it more difficult to predict what the effects will be, and increase your risk of causing a crash.

Mixing drugs increases the danger

Using cannabis with other drugs, including alcohol, reduces your ability to drive safely. A small dose of cannabis can increase the effects of a low blood alcohol concentration.

Some medicines prescribed by a doctor or bought from a supermarket or pharmacy can also increase the effects of cannabis.

Cannabis and driving

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.

If you take cannabis, you won’t be able to drive safely as THC will affect your:

• alertness
• ability to concentrate and judge distances  
• coordination
• reaction time.

These effects can last for hours after taking cannabis and affects everyone differently depending on:

• the amount taken
• your experience with the drug
• your physical and psychological state
• when you last used cannabis.

Research shows you increase your risk of crashing if you drive soon after taking cannabis. Also, if you combine cannabis with alcohol, the risk of crashing is higher 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.  

Drug testing  

Victoria Police test for drugs at the roadside by taking a saliva sample. If drugs are detected, a laboratory test is done. More than one type of drug can be detected in a test, showing a combination of drugs.

It’s an offence to not:

• stop at a random drug testing station
• provide a saliva or blood sample
• cooperate with police who are trying to carry out a saliva, blood or urine test or
• cooperate to take part in a drug impairment assessment.

Some drugs hang around for a long time

Some drugs can be detected in your saliva days after you took them even if you feel you’re okay to drive.

The detection time varies depending on the type of drug, the amount taken, frequency of drug use, and other factors that vary between individuals.  

Plan ahead

Don’t use cannabis or any other drug if you’re going to drive.

Avoid drug driving by planning ahead:

• designate a non-drinking and non-drug taking driver
• hire a taxi or ride share
• use public transport
• stay the night (make sure you’re not still over the limit in the morning)
• arrange for someone to pick you up
• only accept a lift if you’re certain the driver has not been drinking or using other drugs
• always have a plan B if plan A goes amiss.

Law in detail

The laws regarding driving with alcohol and drugs are published in the Road Safety Act 1986. Refer to Part 5 - Offences involving alcohol or other drugs.