Many legal drugs can cause drowsiness, sedation, or impaired coordination, which can impair your driving. Examples include some prescription painkillers, tranquilizers, and antidepressants; and some over-the-counter sleep aids, allergy medications, and cold medications. Taking such a drug together with alcohol can produce greater impairment than either one alone. If you are uncertain about the effects of a drug you are taking, check the warning label or ask your pharmacist or doctor.