Prescribed medicines and illegal drugs when driving

Many prescribed medicines and illegal drugs can affect strongly the ability of driving.

It is important to consult the doctor when a new medicine is prescribed and also it is very useful to read the patient information leaflet to know possible negative effects of a medicine related to the ability of driving. For example, many medicines to treat flu, allergies, colics, anxiety, depression and nervous tension, vasodilators, painkillers, and so on,  may cause sleepiness, visual disorders and other symptoms that will affect your way of driving.


Law says that, “the consumption of drugs hinders to drive when it affects normal parameters of driving, when it causes sleepiness, fatigue or alteration of the motor coordination, attention, sensory perception or good judgement”. But it is important to know that, not only in the case of alcohol but also in the case of drugs, the first psychological effects are also dangerous. The lack of inhibition, an increase of self-confidence and the overestimation of the own ability, with the subsequent underestimation of the danger, are symptoms that can´t be seen, but encourage the driver to behave in a risky way (to speed up, to overtake in a daring way and so on).


Illegal drugs that cause addiction after their repeated consumption, such as cannabis, cocaine, ecstasy, etc., affect driving because they always modify, to a greater or lesser extent, the psychophysical functioning of the person altering, among others, sensory perception, attention and, frequently, motor coordination, apart from distorting risk perception. Together with alcohol, they are a fatal cocktail when driving, since their toxic effects are reinforced.  


Attention! The psychotropic drugs can affect driving!

Their main effects are:

  • Anxiolytics, of common usage as tranquillisers or sleeping pills (especially the benzodiacepines), can cause confusion states, muscular fatigue, decrease of the capacity of concentration and somnolence.
  • Antipsychotics or neuroleptics (for example: thioridazine, haloperidol h.) cause somnolence as their most common effect and extrapyramidal reactions such as muscular spasms, excitement, lack of motor coordination, an so on.
  • Antidepressants (for example, amitriptyline) and antiepilectic drugs (for example, phenobarbital) can affect attention and the state of alert.


As well as psychotropic drugs, there are other medicines that may affect driving. Among them:

  • Some antihistamine, type H1 first generation (for example: chlorpheniramine, diphenhydramine, clemizole), which are very used to ease flu symptoms or colds and allergies, can cause somnolence.
  • NSAIDs –very used for easing muscle or rheumatic pains-, anaesthetics and muscle relaxants can affect, especially, the sense of sight and the attention as well as causing somnolence. Muscle relaxants can also cause decrease of muscle tone and dizziness.
  • Some medicines for heart, especially cardiac glycosides used for certain cardiac crisis, can cause somnolence and alter the state of consciousness and sight.
  • Some antihypertensive, beta-blockers (eg propranolol, nebivolol), to treat high blood pressure can cause somnolence and psychic and equilibrium alterations.
  • Some medicines to sedate cough (for example, codeine) or anti-diarrheals medicines can produce alterations such as attention disorders, decrease of reflexes and others.


These are just some of the medicines that can affect driving.

Consult your doctor and read patient information leaflets to know if the medicine you are taking can affect your capacity to drive.