Aspartame is made from aspartic acid and the methyl ester form of phenylalanine.
Upon digestion, aspartame is completely broken down into its components - the amino acids aspartic acid and phenylalanine, and methanol - which are then absorbed into the blood. Aspartame itself does not enter the bloodstream. The components are then used in the body in exactly the same ways as when they are obtained from common foods and beverages. Neither aspartame nor its components accumulate in the body over time.
The amount of aspartic acid, phenylalanine, and methanol produced during the digestion of aspartame is small compared to that which is obtained from everyday foods. In fact, a glass of tomato juice provides more than 3 times as much methanol as an equal amount of beverage sweetened with aspartame. A serving of skim milk provides nearly 7 times more phenylalanine and 14 times more aspartic acid than the same amount of beverage sweetened with aspartame.