Drivers unfit to steer their vehicles form a major road hazard and they commit a crime. In February 2016, 423 students from Bangor University (Wales, UK) took part in a questionnaire study. They have been asked if they would be driving a car after a) drinking alcohol and b) when taking prescribed medication coming with a warning not to drive. A variety of variables are considered to explain the inclination to drive under those conditions. They include the inclination to engage in imprudent behaviour, perceived dangerousness of driving, and perceived legitimacy of the law. The results suggest that while inclination towards imprudent behaviour affects driving under the influence of medication, driving under alcohol is related to perceived general dangerousness of driving. Driving under medication is also related to legitimacy of law; the difference may come from how public discourse deals with the two types of behaviour.