Phenylalanine by itself is an amino acid. Combined in the lab, unnaturally, with aspartic acid, it creates NutraSweet.

From:

http://www.americanfreepress.net/Alternative_Health/Fake_Sweetener_...

Another form it is found in is one of the components of Aspartame or NutraSweet, which is made of two amino acids, phenylalanine and aspartic acid.

Aspartic acid is an exitotoxin that is as powerful as glutamate. Phenylalanine is an amino acid that is known to produce seizures and act as a neurotoxin at high levels in the brain as well.

Can naturally occurring proteins be harmful to the brain?

The way things are arranged in nature, almost all of the amino acids occur as whole proteins, so that the body slowly assimilates it and breaks it down and converts it in the liver. The level or concentration of their amino acids is always kept at moderately low levels, so that the brain is not assaulted by these dangerous proteins.

When we start manipulating foods and drinks and creating sweeteners that contain high levels of these amino acids in isolation, the blood levels can get quite high, in fact, tremendously high. This results in a significant elevation of these amino acids in the brain and that’s what has most of us worried. It’s at a level high enough to produce destruction of certain groups of brain cells and produce disease, seizures or even death.

I have dropped all pills except for intestinal formula 1. I'd use SuperFood.