From
WebMD:
It is illegal to drive or to attempt to drive while impaired by alcohol or drugs. This is because drinking alcohol, or taking illegal drugs or some prescription medicines, can affect someone’s ability to drive safely. This summer, the government plans to update and clarify the law about ‘
drug-driving’. It will state exactly which drugs are affected, and it will be an offence to drive if you have taken more than a specified level of that drug.
Although the list of drugs affected by the law will still mainly contain so-called ‘recreational’ drugs - things like cannabis, cocaine, heroin, and ecstasy - there are some names on it that people will recognise as medicines. The prescription medicines on the list include methadone, morphine, and benzodiazepines including diazepam and temazepam.
People taking medicines prescribed by their doctor shouldn’t have any difficulty. The new law will state that people who take prescription drugs will have a legal defence (that means it’s not likely they will be prosecuted) as long as:
--they haven’t been taking more than the recommended dose of their medicine, and
--they haven’t gone against the advice about their medicine given in the manufacturer’s information leaflet.
Doctors are already well aware of which prescription drugs can affect people’s ability to drive - usually by making them drowsy. And doctors should make sure people who use these prescription medicines know about how these drugs might affect them.