Cannabis and driving
Health risks, road safety and legal aspects
Cannabis use can impair fitness to drive and is therefore a relevant topic for road safety and public health. Under the influence of cannabis, attention, reaction time, coordination and the ability to assess risk may all be reduced. Even small amounts can impair driving safety — especially in combination with alcohol or other substances.
Health and safety considerations
From a health perspective, the focus is not only on individual accident risk, but also on the protection of other road users. Research shows that acute impairment occurs primarily during the first hours after use. The duration and intensity of effects depend, among other things, on:
- Form of use and THC content
- Amount used
- Individual tolerance
- Frequency of use
- Combination with alcohol, medication or other drugs
With regular use in particular, active substances can be detectable in the body for longer, even when no acute impairment is present. This is a challenge from both a health and a legal perspective.
Legal situation in Switzerland
In Switzerland, a zero-tolerance policy for THC applies in road traffic. Even very small amounts in the blood can lead to administrative and criminal consequences, regardless of whether actual unfitness to drive was present. Possible consequences include:
- Driving licence withdrawal
- Fines or custodial sentences
- Traffic-medical assessments
It is therefore important for people who use cannabis to be informed about the legal provisions and the possible consequences.
Prevention and harm reduction
In the spirit of Cannabis Care, the focus is on information, personal responsibility and risk reduction:
- Do not drive a vehicle after use (car, motorbike, e-bike, scooter etc.)
- Clearly separate use and driving in time
- Avoid mixing with alcohol
- Use alternative transport
- Be especially careful with medical cannabis or regular use
The goal is to reduce risks for people who use cannabis and for the wider public, and to provide evidence-based information.
Research and knowledge gaps
The relationship between THC concentration, consumption behaviour and actual driving impairment is the subject of ongoing research. Open questions include in particular:
- Appropriate limit values
- Distinction between acute impairment and longer-lasting detectability
- Effects of medical cannabis
- Evidence-based prevention strategies
Swiss Cannabis Research is committed to processing scientific evidence and contributing to a more factual discussion.
The universities of Bern and St Gallen, together with ETH Zurich, are currently running a joint driving study on the objective detection of cannabis-related driving impairment using machine learning. Find out more about the study and how to take part here.