Nathan Birch
Mercury, as we now know, is toxic as hell. Symptoms of mercury poisoning include chest pains, heart and lung problems, coughing, tremors, violent muscle spasms, psychotic reactions, delirium, hallucinations, suicidal tendencies, restless spleen syndrome, testicular twisting and anal implosion. OK, we just made the last few up, but they barely looked out of place on that horror show list of symptoms did they?
It's a testament to just how cool a substance Mercury is that people kept trying to cure shit with it for 1,000 years after everybody who ingested it dropped dead. "Yes my Lord, I'm afraid another member of your court has perished. The autopsy showed it was Silver Liver Syndrome. Not even the gallons of wicked-awesome Mercury we fed him could bring him back to health."
There was a silver lining, though, as it helped to fight the spread of STDs. Mercury was used as a cure for syphilis and to its credit, the "cure" usually resulted in one less person with syphilis in the world. It's generally believed Mozart was poisoned by mercury-based syphilis cures, which contradicts the film Amadeus in which he was killed by writing too much music somehow.
Heroin, by the way, was originally 
Perhaps the best part of this is that while most of the practices listed in this article have long since been dismissed as lunacy, urine therapy lives on to today (for your own sanity don't do a Google search for it). That's right, of all the crackpot theories listed here the one that endured is the one where people drink and bathe in piss.
Now, a person having too much blood may sound about as absurd as a person breathing too much air or you coming home to find too many naked supermodels in your bed. But, that's just because you don't know about the four humours. Don't worry, we won't hold your ignorance against you. Basically the theory was that the body was filled with four fluids (blood, phlegm, yellow bile and black bile) called humours and that any imbalance in the four was the root of all illness. Apparently blood can be a bit of a space hog and thus often some had to be bled out to make room for more fun stuff like phlegm and black bile (a.k.a. diarrhea), or so the theory went.
Historically trepanation was most commonly used as treatment for seizures and migraines. Surprise, surprise. Having a gaping hole drilled in your skull (usually without anesthesia) did very little to help people's headaches or brain issues. Trepanation was also used as an extreme form of cosmetic/experimental body modification amongst several societies such as the Incans and Mayans. These societies also got largely wiped out, then a few hundred years later suffered the indignity of having an insulting Mel Gibson movie made about them, so it didn't really work out that well.
So, how exactly do you cure a so-called "condition" that coincidentally was diagnosed almost entirely to women who dared disobey their Victorian husbands? Glad you asked. The prescription for female hysteria was usually a good spot of doctor administered vaginal massage until the woman achieved "hysterical paroxysm."
