1 of 3 chemicals found in Aspartame, the other 2 being aspartic acid and methanol. High levels of phenylalanine in the blood can cause reduction to serotonin levels in the brain, which can cause a person to be short-tempered, bipolar, and even depressed and suicidal.

n. one of two amino acids found in the artificial sweetener aspartame. look on the back of any diet soda bottle.