Drugs - What is the effect of drugs and medicines on the ability to drive?

Driving simulator research shows that the effect of drugs and medicines on driving ability varies by type of drug and even within one type of drug there are differences in the effects [5] [6]. The table summarizes the possible effects of the various drug types.

Cannabis makes users 'high' or 'stoned' which leads to reduced skills on complex driving tasks that require dividing the attention between different aspects of the task. However, cannabis users seem aware of the reduced skills and try to correct for this. The adverse effects may therefore be smaller than expected. However, cannabis used in combination with alcohol leads to a further reduction of skills, because the adverse effects of both substances reinforce each other [7] [8].

Stimulant drugs can cause overconfidence, whereas at the same time the control of the vehicle lessens [6] [9].

Medicines can also affect the ability to drive. Medicine use in the Netherlands is below the European average. This is possibly the result of the strict policy in the Netherlands regarding the prescription of medicines [4]. In the Netherlands, the medicines found to be used by drivers are mainly benzodiazepines (sleeping pills and tranquilizers, anti-anxiety medication) and SSRIs (antidepressants). The numbing effect of these drugs on the brain affects the ability to drive [4]. As the adverse effects of benzodiazepines in combination with alcohol are extra strong, the use of this combination is discouraged (e.g. [7] and [9]).