Understanding Medicinal Cannabis and Driving in Australia
Medicinal cannabis has become a widely prescribed treatment in Australia for various conditions such as chronic pain, anxiety, and sleep disorders. It can be consumed in different ways, including inhalation via a vaporiser or ingestion of an oil. The active compounds in cannabis, known as cannabinoids, include delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). While CBD does not impair cognition or driving, THC is the psychoactive component that can lead to a “stoned” feeling.
The effects of medicinal cannabis vary depending on how it is taken. When inhaled, the effects typically peak within the first hour and may last up to four to six hours. When ingested orally, such as in the form of an oil, the effects take longer to onset and can last up to 8 to 12 hours due to slower absorption and metabolism.
THC negatively affects cognitive functions like attention and memory. Studies have shown that it impairs driving both in simulators and real-world scenarios, particularly on highways. The impact of THC on driving is roughly comparable to low blood alcohol concentrations. However, this depends on the dose and frequency of use. Medicinal cannabis used for insomnia generally does not cause impairment the next day, and regular users show no driving impairment after 48 hours of abstinence.
Despite its increasing use, many medicinal cannabis products in Australia are legal but unapproved, and their efficacy and safety are not fully understood. This has led to discussions about the rise of medicinal cannabis, its implications, and necessary reforms.
Unlike alcohol, THC can make people more cautious while driving, leading some drivers to drive more carefully or maintain larger gaps between vehicles. However, these strategies may not be sufficient to counteract the impairing effects of THC, especially under complex driving conditions.
CBD does not impair cognition or driving. Most studies on cannabis and driving have involved healthy volunteers with deliberately high doses of THC. Therefore, it is unclear whether people with chronic health conditions experience similar levels of impairment when using prescribed medicinal cannabis.
Legal Considerations for Driving After Taking Medicinal Cannabis
In every Australian state and territory except Tasmania, it is illegal to drive with any detectable amount of THC in your system. Roadside drug testing checks for THC in saliva, but it cannot distinguish between prescribed medicinal cannabis and illicit cannabis. In Tasmania, you can lawfully drive with THC in your system as long as you are unimpaired and your medication was prescribed and dispensed in Tasmania.
Other medications that can impair driving, such as opioids and benzodiazepines, do not carry the same restrictions. You can drive with these medications in your system as long as you are unimpaired and using them as prescribed. Driving while impaired is a separate offence and applies to all impairing substances, including medicinal cannabis.
The discrepancy in how medicinal cannabis is treated compared to other impairing medications has been the focus of parliamentary inquiries and law reform discussions. Victoria has amended its road safety act to allow magistrates to decide whether to cancel a driver’s licence if they test positive for THC, are unimpaired, and have a valid medicinal cannabis prescription. However, it remains illegal to drive in Victoria with THC in your system.
You can lawfully drive if you are using a CBD-only medication, provided you are not impaired.
Safe Driving Practices with Medicinal Cannabis
If you have been prescribed medicinal cannabis, there are practical steps you can take to reduce the risk of impaired driving:
- Speak to your doctor: Let them know you drive, especially if you rely on driving for work or caring responsibilities, or if you work in a safety-sensitive environment. Together, you can discuss whether a product containing THC is appropriate or if a CBD-only product might be more suitable.
- Don’t rely on how you feel: Even if you feel normal, your driving ability may still be compromised. The effects of medicinal cannabis can linger for hours, and the length of time varies based on factors such as dose, administration route, and frequency of use.
- Be aware of penalties: Penalties for driving with THC in your system vary by state and territory, ranging from fines to licence disqualifications and potential jail time for repeat offences. A blood test can detect THC days after use, which could lead to severe legal consequences if involved in a crash.
Roadside drug tests do not check for CBD, so it is important to understand the differences between THC and CBD when considering driving.
What We Don’t Yet Know
Research is ongoing to determine how medicinal cannabis impacts driving in individuals who use it for long-term health conditions such as chronic pain. Scientists are also exploring the development of sensors that can detect cannabis impairment in real time while driving.
Once these studies are complete, we will have a clearer understanding of how medicinal cannabis affects drivers who take it for medical reasons.
For more information on medicinal cannabis and driving, visit the Therapeutic Goods Administration’s medicinal cannabis hub or consult your healthcare practitioner.
Tom Arkell chairs the Cannabis and Driving working group through the International Council for Alcohol, Drugs and Traffic Safety. In the past, Tom Arkell has received consultancy and speaker fees from medical cannabis companies. However, he does not currently have any affiliations, consultancies, or funding from medical cannabis companies.
