Drug-induced illnesses are far more common than people, including doctors, would like to think. Elderly people suffer 9.6 million adverse drug reactions each year alone, although these symptoms show up in younger patients as well.
Many do not realize these reactions -- or "new" disease symptoms -- are in fact caused by a drug they're already taking, as most doctors do not explain possible side-effects to their patients.
For example, these common illnesses can be caused by pharmaceutical drugs:
Depression -- Accutane, Advil, Cipro, Inderal, Pepcid, Tagamet, Zantac
Psychoses/Hallucinations -- Benadryl, Celebrex, Dexatrim, Vioxx
Dementia -- Aldomet, Inderal, Tagamet, Xanax
Parkinsonism -- Cardizem, Haldol, Elavil, Risperdal, Thorazine