Drugs That Can Impair Your Thinking

Analgesics (codeine)
Antiarrhythmic drugs (quinidine)
Antibiotics (metronidazole)
Anticonvulsants (carbamazepine)
Antidepressants (imipramine)
Antihistamines and decongestants (dipenhydramine)
Antihypertensive drugs (propranolol)
Antiparkinsonian drugs (levodopa)
Corticosteroids (hydrocortisone, predinisone)
Muscle relaxants (methocarbamol)
Sedatives (phenobarbital, diazepam)
Cholesterol lowering medications (lipitor)

Adapted from "Brain Fitness" by Robert Goldman.