March 17, 2017

Drugs and driving

police and drug buses

Drug driving is a serious road safety issue.

When you drive under the influence of alcohol or drugs (including some prescription and over-the-counter medications) you pose a danger to yourself, your passengers and others on the road.

Victorian data reveals approximately 18% of drivers and motorcyclists killed on the state's roads tested positive to THC, the active component of cannabis. In the past 5 years, 11% of drivers killed, who were tested, had ecstasy, speed, or crystal methamphetamine ('ice') in their system.2

How drugs impact driving

Even in low doses, drugs can significantly reduce your driving skills.

If you’ve taken cannabis, you may drive too slowly, find it difficult to stay awake, or to stay within designated lanes while driving.1

Amphetamines and ecstasy can lead to speeding or erratic driving as well as reduced vision and increased risk taking behind the wheel. 1

Prescription medication

If you have taken prescription medication, whether legally or illegally, you should be aware of the potential risks while driving. If you are feeling drowsy, aggressive, dizzy, nauseous, light-headed or shaky, it can be dangerous to drive as this may for instance impair your vision.

If taking prescribed or over-the-counter medication, always:

  • Read the labels carefully and obey the directions and warnings
  • Ask a doctor or pharmacist if it’s likely to affect your driving
  • Arrange alternative transport.1

Mixing drugs and driving

The impact of mixing drugs can be unpredictable – it’s often difficult to know how combinations of drugs will interact.

This includes the mixing of illegal and legal drugs, but also combinations of legal drugs such as consuming alcohol while taking over-the-counter or prescription medication.

The risk of having a crash while under the influence of 2 or more drugs may even be higher than if a person is under the influence of a single drug. For example, if alcohol and cannabis are used together, impairment in driving ability can be much greater and occur more quickly than if using either one just on their own.4

How driving is affected by combining drugs

The effects of any drug (including multiple drugs) vary from person to person. The impact depends on a range of factors including the person’s size, weight and health, the regularity with which the drug is taken, and if it is consumed in combination with other drugs.

These factors make it difficult to predict exactly, and in what way, mixing drugs may affect a person's ability to drive safely.

As a guide, some of the effects of mixing drugs are outlined below.

Combining drugs with similar effects

Combining drugs with similar effects can increase the impact of each drug. This can place greater strain on the organs in your body, and increases the risk of overdose. Drugs with similar effects include: alcohol and cannabis, alcohol and benzodiazepines, or amphetamines and ecstasy .

Depressant drugs such as alcohol, cannabis, heroin (and other opiates), and benzodiazepines ‘slow down’ the activity of the central nervous system.

Combining different depressants can multiply this effect and can lead to:

  • reduced reaction times
  • reduced concentration
  • drowsiness
  • difficulty processing information
  • difficulty doing more than one thing at a time (e.g. keeping your car within its lane while watching for oncoming traffic).

Stimulant drugs such as amphetamines, cocaine and ecstasy ‘speed up’ the activity of the central nervous system.

Combining different stimulants can multiply this effect. This puts a greater stress on the body, particularly the heart and other vital organs and can lead to:

  • attention difficulties
  • tendency to fidget
  • aggressive and dangerous driving
  • increased risk taking
  • over-confidence in driving skills.

Psychedelics such as ketamine, LSD, magic mushrooms, mescaline and PCP distort a person's perception of reality. Ecstasy and cannabis can also have some hallucinogenic effects.

Taking these drugs can lead to you seeing or hearing things that aren't really there, or experiencing real things in a distorted way.

The effects of psychedelics vary, and combining two or more drugs of this type can have unpredictable effects on driving ability.

As a general guide, some of the effects of combining psychedelic drugs include:

  • hallucinations
  • confused thinking
  • blurred vision
  • reduced coordination.

Combining drugs with different effects

Combining drugs with different effects reduces coordination and hinders your ability to drive. Some examples include mixing alcohol with ecstasy, or cocaine with benzodiazepines.

If you’ve been drinking alcohol and using amphetamines, you may not feel the depressant effects of the alcohol, as it is masked by the stimulant effects of the amphetamines.

You may feel capable of driving, but in reality you might be intoxicated.

Tips for safer driving

If you intend to use drugs, the safest option is not to drive.

Alcohol and other drugs can continue to affect you long after the immediate impact of the substances appears to have worn off. People with drugs in their system continue to pose a higher road risk even if they feel it’s safe for them to drive.3 In addition, people may also feel tired or hung over as drugs wear off, which can also impair their driving ability.

All drivers, whether young or old, should avoid driving if they have recently consumed alcohol or other drugs to reduce the risks.

Speak to a health professional and read the packaging information or a Consumer Medication Information sheet (CMI) before mixing medications, alcohol or other drugs.

Tell your doctor about all the drugs (including prescribed, over-the-counter and illegal drugs) that you use. This can help them to minimise the risk of unwanted interactions between drugs.

Plan ahead

Strategies to avoid drug driving and to stay safe:

  • organising a driver who will not have drugs in their system
  • arranging for a friend or family member to pick you up
  • using public transport or a taxi
  • arranging to stay overnight.

Taking drugs can continue to affect you the next day. Tiredness, hangovers and 'coming down' can also affect your ability to drive safely.

  1. Stough, C. & King, R. (2010). Drugs and driving. Prevention Research Quarterly, 12, 1–32.
  2. Transport Accident Commission. (n.d.) Drugs and Driving.
  3. Monash University Accident Research Centre. (2007). Going Solo - A resource for parents of P-plate drivers
  4. Mallick, J., Johnston, J., Goren, N. & Kennedy, V. (2007). Drugs and Driving in Australia: a survey of community attitudes, experience and understanding. Melbourne: Alcohol and Drug Foundation.

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