Because of the risks associated with barbiturate abuse, and the availability of safer drugs such as the benzodiazepines, barbiturates are less frequently prescribed today than in the past. Nonetheless, they are still available, both on prescription and illegally. Even at moderate doses, they affect motor skills, coordination, vision, and vehicle handling ability. Narcotics Single doses of narcotics can have marked effects on performance, such as reaction time. However, epidemiological and other data suggest that narcotics do not present a hazard or exist as a significant factor in automobile driving.
Some drugs have depressant side effects along with their main medical effect.
Included in this category are cough medicines, cold remedies, drugs to prevent motion sickness or nausea, and antihistamines to control allergy symptoms. Taken on their own, but especially when combined with alcohol, they can cause drowsiness, slower reaction times, and decreased attention and coordination. Cannabis Experimental evidence indicates that cannabis impairs the skills important for driving. Perception and attention are greatly affected and various tracking functions are also impaired. Tests on driving simulators showed the biggest impairment caused by cannabis was in perceiving and responding to potentially hazardous situations.