It's said that China's first emperor Qin Shi Huang was buried in a tomb ringed by rivers of liquid mercury, which is kind of ironic since he died after he ingested toxic amounts of the heavy metal trying to make himself immortal. That immortality plan obviously didn't work out -- he didn't live to see 40.
Mercury has been used as an antiseptic and for treating skin diseases, and has been compounded in everyday products such as saline solutions and cosmetics. If you were unfortunate enough to suffer from syphilis before penicillin hit the scene in the 1940s, your doctor would probably treat your STD with mercury, prescribing for you a mercurial -- ointment, pill, or potion -- to cure the problem. However, mercurials introduced a whole new set of problems, everything from tooth loss to damage to organs (often liver and kidney) and the central nervous system to the biggest problematic side effect of all: death.