"Aspartame is an artificial, non-saccharide sweetener used as a sugar substitute in some foods and beverages. In the European Union, it is codified as E951. Aspartame is a methyl ester of the aspartic acid/phenylalanine dipeptide. It was first sold under the brand name NutraSweet; since 2009 it also has been sold under the brand name AminoSweet. It was first synthesized in 1965 and the patent expired in 1992.
The safety of aspartame has been the subject of several political and medical controversies, congressional hearings and Internet hoaxes since its initial approval for use in food products by the U.S. Food and Drug Administration (FDA) in 1974. A 2007 medical review on the subject concluded that "the weight of existing scientific evidence indicates that aspartame is safe at current levels of consumption as a non-nutritive sweetener". However, because its breakdown products include phenylalanine, aspartame must be avoided by people with the genetic condition phenylketonuria (PKU)."
The above is the cuddly view. For a sterner opinion, and for some shocking reports on the DANGERS of diet drinks etc....
http://www.documentaryz.com/c9-health/1931-sweet-remedy-adulterated-food-supply/
[unputdownable, if it were a book]
To avoid ALL the dangers of sugar, but get all the sweetness (without the carbs!) Why not try 'Stevia'...
http://www.stevia.com/