A new drug driving law is to come into force on 2 March 2015* that will make it illegal to drive with certain controlled drugs in the body above specified limits. 16 drugs are specified in the new legislation, including illegal drugs such as cannabis and some medicinal drugs. Police will now have powers to obtain blood samples from drivers to test for the presence of these substances.

A panel of medical and scientific experts advised on the eight medicinal drugs that are most associated with road safety risks. They are grouped as follows: clonazepam, diazepam, flunitrazepam, lorazepam, oxazepam, and temazepam; methadone and morphine; and amphetamine and substances that can metabolise into amphetamine such as selegiline.

The testing limits for the majority of these medicinal drugs has been set above normal dosage levels, and the Department for Transport (DfT) has reassured patients and pharmacists that most people taking these medicines in accordance with the advice of a healthcare professional or as advised in the accompanying leaflet are unlikely to be affected.

*This applies to England and Wales only. The law will be introduced in Scotland at a later date to be confirmed by the Scottish government.