Aspartame

It is 160 times sweeter than sugar (sucrose), and is marketed under a number of trademarked names, such as "NutraSweet" and "Canderel". It is a common sweetener in prepared foods, particularly soft drinks. Aspartame is one of the sugar substitutes used by diabetics.
Because phenylalanine is part of its composition, and is deleterious to sufferers of the genetic disorder phenylketonuria, products containing aspartame usually have a warning label that they contain phenylalanine, in compliance with U.S. FDA guidelines. Aspartame breaks down at a lower temperature than other artificial sweeteners, and is unsuitable for use in baking or to sweeten coffee and tea.

One of the (many) hypotheses about the causes of Gulf war syndrome is that the soldiers, drinking huge quantities of fluids (soft drinks) in the extreme heat, accumulated toxic doses of methanol, formaldehyde, diketopiperazine[?] and formic acid from the breakdown of aspartame into its component molecules. However, the symptoms do not greatly resemble those of classic methanol poisoning, and the body, in its normal metabolism, produces methanol in quantities comparable or greater than would be ingested via aspartame, so this theory does not have wide support.