Driving is a complex task which requires full concentration. Driving while under the influence of alcohol or other drugs can seriously affect your ability to drive safely.
In Australia 30% of fatal road crashes are a result of drink driving and 1 in 4 drivers/riders killed on roads have a blood alcohol concentration (BAC) above the legal limit (0.05). Research shows that driving under the combined influence of alcohol and illicit drugs make it 23 times more likely a fatal crash will occur. See below for information on how different drugs can affect your driving.
Alcohol is a depressant drug, meaning it slows down your central nervous system including your brain. As such, alcohol can impact your ability to judge distances correctly, decrease reaction time, reduce your ability to concentrate, reduce sensitivity to red lights, and higher BACs can give a feeling of euphoria leading to increased risk taking, reckless driving, and overestimation of driving abilities.
Cannabis has stimulant, depressant, and hallucinogen effects. THC (Delta-9-tetrahydrocannabinoil), is the main active ingredient in cannabis and responsible for the drug’s ‘high’. Studies have found direct relationships between blood THC levels and impaired driving ability. Cannabis can significantly affect your motor coordination, slow down thinking and reflexes, and reduce concentration and coordination.
Opioids (e.g., Heroin)
Heroin is a depressant drug. Heroin slows down reaction time when driving and makes it hard to properly judge distance and speed. It also makes it difficult to concentrate, greatly increasing the risk of having a car crash.
LSD, Acid, and Magic Mushrooms
These drugs are known as “hallucinogens” and affect your body by altering your sight and hearing, making it harder to judge distances and speed when driving. Hallucinogens can also slow down your reaction time.
Methamphetamine (Ice), MDMA/Ecstasy, and Cocaine
These drugs are known as “stimulants” and increase activity in the central nervous system. Driving under the influence of stimulants can lead to a false sense of confidence, rash decision making, and risk taking. Stimulants can make it hard to sleep causing tiredness which can greatly affect concentration and reaction time when driving.
Taking illegal drugs before driving puts you at greater risk of injuring or fatally injuring yourself, your friends, or other innocent people.
Driving laws and limits
In Australia police use your blood alcohol concentration (BAC) to measure the amount of alcohol in your body and determine how intoxicated you are. The most common way to measure BAC is through a breath test using a breathalyser. Blood tests can also be used if you are admitted to hospital after a motor vehicle accident and are unable to provide a breath test.
A BAC measures grams of alcohol present per 100mL of blood, for example a BAC of 0.05 means there is 0.05g of alcohol per 100mL of blood. For full license holders, it is illegal to drive a motor vehicle with a BAC above 0.05%. However, when you hold a Learners or Provisional driver’s license all states and territories require you to have a BAC of zero (0.00). There is no level of drinking which will guarantee a BAC under 0.05, however, drinking less than 1 standard drink per hour will keep most people’s BAC under 0.05%. Trying to calculate or guess your own BAC based on the number of drinks you’ve had is difficult and often inaccurate because everyone’s bodies are different and there are many factors which can affect your blood alcohol concentration.
Factors that can affect BAC include:
- How quickly you’ve been drinking and the amount of alcohol you’ve drank
- Your body size including height and body fat percentage
- Your sex
- The amount of alcohol you’ve been drinking
- The amount of food in your stomach
- Any medication you are taking
- How often you drink
When drinking large volumes of alcohol, you can still have alcohol present in your system the next day.
Myth: You can sober up quicker by drinking coffee, having a cold shower, vomiting, eating bread/fatty foods etc.
The truth is the only thing that will sober you up and lower the concentration of alcohol in your bloodstream is time. After alcohol enters the stomach, it’s quickly absorbed into your bloodstream. Here your body has to work hard to breakdown the alcohol which takes time and energy. Things such as drinking a glass of water or coffee can help with the dehydrating effects of alcohol, but do not impact your BAC.
In all states and territories, it is illegal to drive a vehicle while under the influence of drugs. Roadside drug testing in Australia targets illicit drug use, but it’s important to remember some prescription drugs can also affect your driving.
Random roadside drug testing uses saliva samples to detect illicit drugs. These tests can detect:
- THC (Delta-9-tetrahydrocannabinoil), the main active compound in cannabis responsible for the drugs ‘high’.
- Methamphetamine, which is found in drugs such as ‘ice’, ‘speed’, ‘base’, or ‘crystal meth’.
- MDMA, also known as ecstasy, ‘caps’ or ‘pingers’.
If the presence of drugs is detected from a saliva test you can then be subject to further testing. Because saliva tests don’t detect all drugs police can request an oral fluid test, blood test, or urine test. These tests will be sent to a laboratory and can detect the presence of any illicit and/or prescription drugs. Please note drug testing differs around Australia, refer to state and territory Government websites for location specific information.
Remember that it is not just illicit drugs that can affect your ability to drive safely. Over the counter medicines and herbal remedies, some of which can be available in supermarkets, can also affect your driving. Read all warning labels and if in doubt seek medical advice.
Penalties for drink driving and driving under the influence of other drugs differ between states and territories. Penalties can include immediate loss/suspension of licence, vehicle impounding, installation of an alcohol interlock (electronic breath testing device which must be used before your vehicle starts), good behaviour programs, prison sentences, and a criminal record. There are also penalties for failing to comply (refusing) alcohol/drug testing requirements. Combined drink and drug driving offences normally have higher penalties.
See below for specific state and territory information.
Road safety and staying safe
If you’re going to be drinking plan not to drive. Try and arrange how you’ll get home before you head out. Some options might include:
- Public transport
- Rideshare services such as Uber, Ola, Didi, and Sheba (an all women rideshare company)
- Friend or sibling
- Parent or caregiver.
This factsheet was developed following expert review by researchers at the Matilda Centre for Research in Mental Health and Substance Use at the University of Sydney.
The information is a general summary and should not be taken as comprehensive legal advice. If you have been charged with a drug offence you should contact a criminal lawyer for assistance.