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The facts about roadside drug testing

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Driving a motor vehicle safely is a complex task. We must be mentally alert, have clear vision and good physical coordination. This allows us to pay close attention to many things at once, and to react quickly when something unexpected happens. Taking drugs or other substances that affect the brain can reduce the ability to drive safely.

It is an offence to drive if you are under the influence of alcohol or other drugs and do not have proper control of your vehicle. Keep in mind that if you have taken alcohol or other drugs it is difficult to assess how much your own driving skills have been affected.

If you intend to drive, the safest option is not to have any alcohol or other drugs in your system at all. This includes any prescription medicines that affect your driving ability. It is also important to remember that fatigue, and the after-effects of drug use "coming down", can affect your driving skills.

This fact sheet explains drug testing of drivers in Victoria, and the steps you can take to stay safe.

What is drug testing?

Drug testing looks for traces of drugs in the body using samples of urine, breath, hair, saliva, or sweat. Testing may be used to detect illegal drug use, as well as the use of drugs not permitted while driving, or in specific workplaces or sports.

Passing a drug test may mean that either the drug is no longer in your body, or that the test cannot detect the traces that remain.

What types of types of drug tests are used?

Standard Impairment Assessment (SIA)

In Victoria, police use the Standard Impairment Assessment (SIA) to test drivers they believe may be under the influence of drugs. The test will show impairment equal to, or higher than, a blood alcohol concentration (BAC) of 0.05.

There are four parts to the assessment:

  1. Interview and observation
  2. Physical impairment test
  3. Walk and turn test
  4. One leg stand test

Saliva tests

Random roadside drug testing, in Victoria and most other states and territories, uses saliva samples to detect illicit drugs.

A sample of the driver's saliva is taken by specially-trained police officers, using an absorbent collector placed in the mouth or touching the tongue. This test takes about three to five minutes. If the test is positive, it must be confirmed by laboratory testing before charges can be laid.

In Victoria, roadside saliva tests detect drugs that contain:

  • THC (Delta-9 tetrahydrocannabinol), the active component in cannabis
  • methamphetamine, which is found in drugs such as "speed", "base", "ice", and "crystal meth"
  • MDMA (Methylenedioxymethamphetamine), which is known as ecstasy.

These tests do not detect the presence of legally prescribed drugs or common over-the-counter medications.

Breath tests

Over many years, police have carried out extensive breath testing of Australian drivers to detect the amount of alcohol in their system. The procedure is straightforward—the driver is instructed to blow into a hand-held breath-testing device until deep lung air is exhaled. The BAC reading is given on a digital display.

Acceptable BAC limits vary for different types of driving licences, and in different areas of Australia. Contact your local authority or road safety agency for more details on how these laws affect you.

How long will drugs stay in my system?

Drugs and alcohol affect every person differently, so drug testing results will be unique to each individual.

Results can be affected by:

  • The strength of the drug or alcohol
  • How much you have taken
  • How you have used it
  • How often you have used it
  • Other drugs you have taken

Results can also be affected by your:

  • Tolerance
  • Sex and age
  • Overall health and wellbeing
  • Metabolism
  • Mood, and the environment you are in

How long can they be detected?

Cannabis: Random roadside drug testing can detect THC (the active ingredient in cannabis) for at least several hours after use. The exact time can vary, depending on the amount and potency of the cannabis used and the individual's metabolism. Inactive THC residue in the body of a driver from use in previous days or weeks will not be detected. However there have been reported cases of people testing positive to cannabis a number of days after consuming.

Methamphetamine ("speed", "ice") may be detected for approximately 24 hours after use by random roadside drug testing and is dependent upon the amount and potency of the drug and the individual's metabolism. Note that the withdrawal effects of methamphetamine, such as fatigue, anxiety and irritability, can also lead to unsafe driving.

MDMA (ecstasy) may be detected for approximately 24 hours after use by random roadside drug testing. The exact time will be dependent upon the size and potency of the dose, if other drugs are used at the same time and the individual's metabolism. 

Alcohol: The liver takes an hour or more to break down the alcohol in one standard drink. A standard drink is equivalent to 10 grams of alcohol, as is found in 100ml of wine. For more information on standard drinks, see the DrugInfo fact sheet, "What is a standard drink?".

It is important to remember that you may still be affected by alcohol the next morning. This is particularly important for drivers required to keep to a zero BAC limit.

If you are taking medication it is best to talk to your doctor about whether you are safe to drive. Also check whether your medication will be affected if you drink alcohol.

Staying safe

The only sure way to test negative on a drug test—other than not taking drugs—is to make sure your body has eliminated all of the drugs you have taken.

Most drugs take at least 24 to 48 hours to leave your body. This means that even if you are not drunk or stoned any more, these drugs can continue to affect your body. If you are taking more than one drug at a time (including drinking alcohol), the drugs may take even longer to be eliminated from your body.

Avoid driving whenever you have been using alcohol or other drugs. Also remember that even if you feel like you are OK to drive, you are still likely to be affected and unsafe on the roads.

If you intend to use alcohol or other drugs and need to travel, plan ahead by:

  • Organising a driver who will not be using any alcohol or other drugs
  • Arranging to be picked up
  • Using public transport or a taxi
  • Arranging to stay overnight

It is important to remember that alcohol and other drugs can continue to affect you the next day. Fatigue, hangovers and "coming down" can also affect your driving ability.

Taking more than one drug

People who have more than one drug in their system will be more impaired, and have a higher risk of having a car accident. The risk is increased when the content and purity of illicit drugs are unknown.

More information

Information in this fact sheet is intended as a general guide only. While care has been taken to ensure that the information contained in this fact sheet is complete and correct, the Australian Drug Foundation (ADF) makes no representation as to the completeness, accuracy, reliability or suitability of the contents of this fact sheet. The ADF does not offer any information in this fact sheet as a tool for treatment or counselling. The ADF recommends that prior to making any decision based on any information in this fact sheet, you should obtain independent professional advice.

For more information on drugs and drug prevention contact DrugInfo.


Last updated: 11 November 2016

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