In March 2015 a new offence of driving with certain, specified controlled drugs in excess of legally defined levels in the body came into effect. This offence is in addition to laws then in force relating to drug (and alcohol) impaired driving and fitness to drive.
The regulations relating the offence contain a statutory ‘medical defence’, which applies to patients taking such medication in accordance with instructions.
There are two broad classes of drug covered by these regulations:
- Commonly abused drugs, which are likely to be prescribed for a very small number of patients, for whom low levels allowed have been set.  The ‘medical defence’ will still be available and it is possible that patients taking these drugs as prescribed may have blood levels about the legal limit.  These drugs include cannabis, cocaine, ketamine and heroin/diamorphine.
- Mainly licensed medicines that have a significant risk of being abused  blood levels for this group are generally about the therapeutic range and so patients taking such medication, in accordance with instructions, are unlikely to have blood levels above the limit.  The ‘medical defence’ is available as it is recognised some patients, for a variety of reasons, will be using the relevant medication as prescribed but have higher than legal blood levels.  This group includes a number of benzodiazepines, such as diazepam, temazepam and lorazepam, and also methadone and morphine.
In either case, if a patient’s driving is impaired, the patient can be prosecuted and there is no ‘medical defence’ for impairment as, whatever their medication, no-one should be driving if impaired.
Patients may find it helpful to carry evidence that they have been prescribed the relevant medication, such as a repeat prescription form.  GPs are under no obligation to provide specific additional evidence, such as a letter confirming the patient’s medication.
Department of Health Leaflet on New Rules - March 2015
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Updated on 22 September 2017