For centuries, this poisonous chemical was taken in a range of forms -- pills, ointments, and inhalation. The one thing they all had in common was that they came with extensive, and long-lived, side effects including kidney failure, mouth ulcers and teeth loss. "We now know it was mercury poisoning," says Stein.
But the poison was considered an effective remedy, particularly against skin diseases. "Mercury was used for everything relating to skin diseases until the late 19th century," says Stein. It was also among the first treatments used against syphilis.