Arsenic poisoning kills by massively disrupting the digestive system, leading to death from shock.

Roger Smith, Professor of Pharmacology and Toxicology Emeritus, Dartmouth Medical School, has stated that natural arsenic contamination of drinking water has been a problem in wells in Bangladesh and New Hampshire. The Bangladesh well poisoning is a particularly difficult problem: millions of people take their drinking water from wells that were drilled through arsenic-bearing rock layers. Chronic low level arsenic poisoning as in Bangladesh can result in the victim developing cancer.

There is a theory that Napoleon Bonaparte suffered from arsenic poisoning, and samples of his hair did show high levels of the element. This, however, does not imply deliberate poisoning by Napoleon's enemies: Copper arsenate has been used as a pigment in some wallpapers, and microbiological liberation of the arsenic into the immediate environment would be possible. The case is equivocal, in the absence of clearly authenticated samples of the wallpaper.

Even without contaminated wallpaper, there are many other routes by which he could have picked up arsenic: arsenic was used medicinally for centuries and, in fact, was used extensively to treat syphilis before penicillin was introduced; it was replaced for treating other conditions by sulfa drugs and then by antibiotics. Arsenic was an ingredient in many tonics (or "patent medicines"), just as coca (unrefined cocaine) was an ingredient in Coca-Cola when it was introduced. During the Victorian era, some women ate a mixture of vinegar, chalk, and arsenic to whiten their skin.

A later case of arsenic poisoning is that of Claire Booth Luce , the American ambassador to Italy in the years just following World War II; she suffered an increasing variety of physical and psychological symptoms until arsenic poisoning was diagnosed, and its source traced to the old, arsenic-laden flaking paint on the ceiling of her bedroom. Another source (http://www.dartmouth.edu/~toxmetal/TXSHas.shtml) explains her poisoning as resulting from eating food contaminated by flaking of the ceiling of the embassy dining room. She did not die from her poisoning.