Rule 96: Drugs and medicines
You MUST NOT drive under the influence of drugs or medicine. For medicines, check with your doctor or pharmacist and do not drive if you are advised that you may be impaired.
You MUST NOT drive if you have illegal drugs or certain medicines in your blood above specified limits. It is highly dangerous so never take illegal drugs if you intend to drive; the effects are unpredictable, but can be even more severe than alcohol and result in fatal or serious road crashes. Illegal drugs have been specified at very low levels so even small amounts of use could be above the specified limits. The limits for certain medicines have been specified at higher levels, above the levels generally found in the blood of patients who have taken normal therapeutic doses. If you are found to have a concentration of a drug above its specified limit in your blood because you have been prescribed or legitimately supplied a particularly high dose of medicine, then you can raise a statutory medical defence, provided your driving was not impaired by the medicine you are taking.
Law RTA 1988 sects 4 & 5
Why the capitals matter. The Highway Code writes a rule in capitals — MUST or MUST NOT — when it is backed by law, so breaking it is a criminal offence. The rules that do not use capitals are advice.
5 theory test questions on this rule
From the DVSA revision question bank. These are not the questions asked in the real theory test. Each one shows the answer, the explanation, and our own note on why every other option is not it.