Medico-legal: The new drug-driving law

The MDU's Dr Nicola Lennard offers tips to understand the law and advice patients may need.

Patients might ask you for written confirmation of prescribing advice, in case stopped by the police (iStock)
Patients might ask you for written confirmation of prescribing advice, in case stopped by the police (iStock)

A new offence of drug driving, which came into force on 2 March 2015, makes it illegal to drive with more than a specified amount of some controlled drugs in the blood.

The law allows for a 'medical defence' for people who have been prescribed medications and are taking them in accordance with the prescriber's advice.

1. Patients may ask for medication evidence

It remains the responsibility of the driver to consider whether their ability to drive is, or may be, impaired and if in doubt, to refrain from driving. However, GPs may be asked by patients about the impact of their medications on their ability to drive and whether they might be prosecuted if stopped by the police.

Patients might ask you for written confirmation of prescribing advice, in case they are stopped or after being stopped by the police.

The new legislation should not affect the way you prescribe the medications in question and it is anticipated that patients taking therapeutic doses of prescribed medication should not be over the specified limit for drugs.

When prescribing, GPs are responsible for ensuring that appropriate advice is provided to the patient about the potential risk of a medication impairing their ability to drive. For example, you will already be advising patients about the risks and side-effects of medications, such as drowsiness.

The government has issued guidance for healthcare professionals to help them explain the new law to patients taking these medicines.1

2. Know the groups of medication involved

There are two groups of medication covered by the new offence - licensed medications and recreational drugs. Common recreational drugs covered by the legislation include cannabis, cocaine, MDMA, LSD, ketamine, heroin/diamorphine metabolite and methylamphetamine. The limits for these recreational drugs have been set at a low level.

The second group are mainly licensed medications, for which higher limits are acceptable in the bloodstream. They include benzodiazepines (clonazepam, oxazepam, diazepam, lorazepam, temazepam), methadone and morphine. Amphetamine may be added to the regulations at a later date.

3. Understand when a medical defence might be requested

It is already an offence to drive while impaired by drugs. This will remain in force alongside the new offence.

However, if the police suspect a driver's fitness to drive may be impaired by drugs, they can stop and screen them at the roadside for the presence of drugs in their saliva.

If the test is positive, the driver may face blood tests, which would identify whether their blood level of the drug is above the new legal limit.

Patients can raise a medical defence if they are taking the medication for therapeutic purposes and in accordance with the advice given by the prescriber.

Patients may ask for a report if they are stopped and tested and found to have exceeded the limit for a medication. Some may also request a report as evidence that they are prescribed the medication, to keep with them in case they are stopped.

If providing a report, you should bear in mind your duty of confidentiality and disclose only the minimum amount of information necessary.

Under existing road traffic offences, the police can still prosecute for driving while impaired by drugs, for which there is no medical defence.

4. Document your advice to patients about medications

The MDU advises that you clearly document the advice you give to patients about their medications.

This is in line with GMC advice requiring doctors to keep accurate and contemporaneous records, including information given to patients.2

You may wish to take particular care to record advice about driving while taking medication, including any written advice, and other factors that may affect the patient's fitness to drive, such as drinking alcohol.

5. Communicate clearly about patients' fitness to drive

If you become aware that patients may be taking more of their medication than is being prescribed, for example, if a patient is requesting repeat prescriptions too often, it would be advisable to discuss the question of fitness to drive with the patient, ensuring this discussion is carefully documented.

You may decide to audit the records of patients on the relevant medications, to see whether advice on driving while taking the drugs is being properly documented.

  • Dr Lennard is a medico-legal adviser for the MDU


1. Department for Transport. Guidance for healthcare professionals on drug driving. July 2014. file/325275/healthcare-profs-drug-driving.pdf

2. GMC. Good Medical Practice 2013, paragraph 21.c

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