In 1964, Dr. Jacob Sheskin was presented with one such unlucky fellow. At the time, the accepted treatment for leprosy was still "hollow caves," but Sheskin decided to give the man a sedative to help him sleep. However, what he gave him was thalidomide, a drug that had been internationally banned because of its unfortunate side effect of producing truly horrific birth defects. Precisely what compelled Sheskin to prescribe a stupendously illegal drug has been lost to the sands of time (we assume he just didn't feel comfortable writing the man a prescription for a bottle of whiskey and a .38).
Shockingly, after three days of shoving doses of thalidomide between the ragged flaps of skin hanging over his teeth, not only was the patient well-rested, but his leprosy had virtually disappeared. By completely ignoring both the law and the oaths of his profession, Sheskin had accidentally tripped over the first effective treatment for leprosy, which is still being used today.
Sheskin (bald, center), pictured here with several other people he regularly dosed with illegal drugs.