Mercury

"The early Chinese believed that medications containing cinnabar and mercury could prolong life. Consequently, several emperors were reputed to have died from mercury poisoning in futile attempts to attain immortality."

"Faith in mercury's magical powers was extended to medicine with new efforts to cure syphilis. Such notables as Napoleon, Ivan the Terrible, Robert Burns and countless kings and noblemen are believed to have been shepherded to the netherworld by mercurialists in vain attempts to cure the dread disease."

From: Mercury Contamination: A Human Tragedy, by Patricia and Frank D'itri, John Wiley and Sons: New York, 1977.