Alcohol, marijuana, and other drugs can impair the ability to drive because they slow coordination, judgment, and reaction times. Cocaine and methamphetamine can make drivers more aggressive and reckless.
Cough and cold medicines. Over-the-counter cold medicines like NyQuil can cause a hangover-like effect in some people, making them feel tired or sluggish for up to eight hours. That's why Smith says you shouldn't drive for at least 12 hours after taking this type of medicine, “just to be safe.”