Once upon a time trepanning - drilling a hole in the skull to "let evil spirits out" - was a common medical practice. We don't do that anymore either, for what I should hope are obvious reasons.

Mercury was once used as a treatment for syphilis, among many other things. Lobotomies, radium "treatment", cocaine and heroin was used as a treatment for children with a cough, smoking was recommended as a treatment for asthma, electroshock therapy was used for damn near everything, induced insulin comas, arsenic and lead, tapeworm diets...

You all get the point.