Arsenic-based medicine, Wm. R. Warner & Co., about 1900 Arsenic was widely used as a medicine in the 19th and 20th centuries. The development of forensic toxicology coincided with the spread of mass-produced and commercially distributed medicines and poisons (sometimes the same thing), and an associated rise in murders and suicides involving those substances. Arsenic is a poisonous metallic element having three allotropes, of which the gray form is the most common. It was first documented by Albertus Magnus. Arsenic is a metalloid.