Photo: Chokniti Khongchum / Pexels. Illustrative photograph.
You can drive on prescribed medicine in Great Britain, even one on the drug-driving list, as long as it was prescribed for you, you take it as advised, and it does not make you unfit to drive. That is the statutory “medical defence”. It does not cover driving while impaired: if a medicine affects your driving, it is an offence whether or not it was prescribed.
The two drug-driving offences
| Over a specified limit | Unfit through drugs (impairment) | |
|---|---|---|
| What it means | A listed drug in your blood above its legal limit, even if your driving seems fine | Any drug, legal or illegal, making you unfit to drive |
| Medical defence? | Yes, for a drug taken as prescribed or advised | No |
| Where it applies | England, Scotland and Wales | England, Scotland and Wales |
GOV.UK says this law does not cover Northern Ireland, but you can still be arrested there if you are unfit to drive. Check the DVA and PSNI guidance if you are learning in Northern Ireland.
Which prescription medicines are on the list?
GOV.UK lists these medicines as covered by drug-driving law:
- amphetamines, such as dexamfetamine (used for ADHD) and selegiline
- clonazepam, diazepam, flunitrazepam, lorazepam, oxazepam and temazepam
- methadone
- morphine and other opiate or opioid drugs, such as codeine, tramadol and fentanyl
Illegal drugs on the list, including cannabis (THC) and cocaine, have very low limits. The limit for THC is 2 micrograms per litre of blood and for amphetamine 250 micrograms per litre, in England and Wales as of November 2026. Police can use a roadside kit to screen for cannabis and cocaine.
How the medical defence works
The Department for Transport’s guidance says the defence generally applies if the drug was:
- lawfully prescribed, supplied or bought over the counter for a medical or dental purpose, and
- taken in line with the advice of the prescriber or supplier and the leaflet, as far as the leaflet matches that advice.
Your prescriber’s advice for you can differ from the leaflet and still count. The guidance suggests carrying evidence that you were prescribed the medicine or bought it, and took it as instructed. You can choose what you show, so you do not have to reveal more than you want to.
Prescribed medical cannabis
GOV.UK’s drug-driving pages do not treat prescribed cannabis separately. The medical defence covers a drug that was lawfully prescribed and taken as advised, and the impairment offence still applies in every case. Ask your prescriber how the defence applies to your medicine and whether it can affect your driving. Cannabis that has not been prescribed for you has no defence at all.
Over-the-counter medicines
Codeine is on the list, and many other medicines that are not, such as some antihistamines and sleep aids, can still make you drowsy. A medicine does not need to be on the list for the impairment offence to apply.
- Read the leaflet for warnings about drowsiness or driving.
- Ask your pharmacist before driving on a new medicine.
- Do not drive to a lesson or test if a medicine leaves you drowsy.
Penalties for drug driving
- a minimum 1-year driving ban
- an unlimited fine
- up to 6 months in prison
- a criminal record
- the conviction shows on your licence for 11 years
A ban means you cannot drive at all for that period, including as a learner. Full limits and drink-drive rules are in drink and drug driving limits.
Back to the GB medical conditions and disability guide. Related: ADHD, autism and dyslexia, anxiety, depression and mental health, fitness to drive and telling the DVLA.
Sources
- GOV.UK, “Drugs and driving: the law” (gov.uk)
- Department for Transport, “Drug driving guidance for healthcare professionals” (gov.uk)
- The Drug Driving (Specified Limits) (England and Wales) Regulations 2014, as amended 2015 (legislation.gov.uk)
- DVLA, “Appendices: assessing fitness to drive”, updated 7 November 2025 (gov.uk)