This article explains the Department for Transport review on medical cannabis and road safety. Prescribing has grown in specialist and private clinics since 2018, which means more patients may lawfully use THC containing products and still need to drive. Below you will find the key points in plain English, plus clear guidance for patients and a link to the source.

Medical cannabis and road safety key takeaways

• THC can impair reaction time, attention, and coordination. CBD on its own does not show driving impairment in current evidence.
• Medical products vary by THC and CBD content. Dose, timing, route, and individual tolerance matter.
• UK drug driving law sets a low THC limit. A medical defence exists for lawful prescriptions, but it does not protect impaired driving.
• Evidence on collision risk for medical users is mixed. Real world UK data is limited.
• The report calls for better data, clearer guidance, and targeted research that reflects typical UK prescribing.

What counts as medical cannabis

The report uses medical cannabis to include licensed medicines and unlicensed cannabis based products for medicinal use, known as CBPMs. Licensed examples include Sativex and Epidyolex. CBPMs may contain THC, CBD, or both, and they can be prescribed in different forms and routes of administration. Over the counter CBD supplements and illicit cannabis are outside scope, though they are noted as context.

What the review set out to answer

1. How common prescribing is in the UK, and who is using these products, including drivers.
2. What the effects are on driving performance and ability.
3. Whether use increases crash risk, and whether that varies by product type or dose.

What the evidence shows

Driving performance

THC can impair cognitive and psychomotor functions. That includes slower reaction time, reduced attention, and poorer coordination. CBD alone does not show impairment in current research. Many studies focus on recreational use and higher doses, which may not reflect typical prescribed regimens. Patients can also develop tolerance, which affects impact on driving tasks.

Crash risk

Findings are mixed. Some studies link THC to higher collision risk. Other studies find little or no effect once dose and tolerance are considered. UK specific research on medical users who take prescribed doses is limited, so firm conclusions for real world medical use remain uncertain.

The UK legal position in brief

• Drug driving law sets a low blood limit for THC, regardless of why THC is present.
• A statutory medical defence exists if you have a lawful prescription and follow dosing instructions.
• The defence does not apply if you are impaired while driving.

Bottom line. A prescription can explain THC in your system, but it cannot excuse unsafe driving.

Evidence gaps highlighted by the report

• Accurate numbers of UK drivers who use prescribed cannabis products.
• Clear separation of medical use and recreational use in analysis.
• Controlled studies at prescribed doses, with timing and tolerance tracked.
• Real world UK data on collisions that involve medical users.

Practical guidance for patients who drive

• Know your product. Check THC and CBD content. Ask your prescriber how this may affect you.
• Mind the timing. Avoid driving soon after taking THC containing products. Give yourself time to assess your response.
• Start low, go slow. If treatment is new, avoid driving until you understand your personal effects.
• Carry proof. Keep evidence of your prescription and dosing instructions.
• Do not drive if impaired. If you feel slowed, foggy, or uncoordinated, do not drive.
• Review regularly. Speak with your clinician about dose, timing, and safer alternatives if driving is essential.

What this means for policy

The report does not call for alarm. It calls for better data and clearer guidance. Likely next steps include improved patient advice on safe driving intervals, stronger collection of prescription and collision data, and research that reflects typical UK dosing. Good policy can protect patient access and protect the public at the same time.

Frequently asked questions

Further reading

• Medical cannabis and road safety, Department for Transport, PDF
• More on medical cannabis