Aspartame has been given a bad name by the media but is it justified? 

The studies that reported negatively on aspartame were on rats and these animal studies show a low level of evidence compared to more robust evidence such as systematic reviews (meta-analysis) and randomised controlled trials. 

Looking at all the evidence, Aspartame has been found to be safe and can be effective in helping with weight control.  For example replacing a sugary drink with the diet version can save 135 kcals and 7 teaspoons of sugar.

Aspartame is a combination of two amino acids, phenylalanine and aspartic acid which are both found naturally in protein containing foods.