The responsibility of psychotropic drugs as a cause of road traffic accidents remains difficult to evaluate with precision. Different studies performed in many countries provide a certain precision in relation to percentage of injured drivers whose blood contained psychotropic substances (8 to 10% according to studies). On the other hand, it is practically impossible to really know either these products were or were not the cause of the accidents because underlying or associated pathologies can equally create problems such as lack of attention and other vigilance deficits. There is also a possibility of suicidal or aggressive tendencies. A certain number of circadian and other chronobiological parameters also complicate the problem since the schedule (hour) as well as the day of the week or even the season can considerably modify vigilance and reaction time. Available medications able to create such problems are numerous and their mechanisms of action varied. They can influence vision, impulsiveness and vigilance. They can act either by direct mechanisms of sedation or, on the contrary, by raising inhibition through secondary mechanisms: delay in drug elimination or provoked insomnia. For the most part, incriminated medications belong to the different classes of sedative medicines: benzodiazepines, antiepileptics, some antihistaminic agents, some antidepressants, some thymo-regulators and some anti-hypertensives. Also included are desinhibitors or stimulant classes: amphetamines and related drugs, caffeine and codeine. Some of them can be used for their psychodysleptic properties: codeine and anticholinergic drugs. Finally, drug and medicinal associations can have unforeseen effects: for example, anticholinergics + alcohol + valpromide, etc. If it appears methodologically impossible that research could ever precisely quantify the share of responsibility of psychotropic drugs in causing road traffic accidents, this relation remains highly probable. It is therefore necessary that in the course of university and post-academic training, potential prescribers might regularly be advised of these risks. Lastly, public needs to be constantly informed.