L-phenyalanine apparently "inhibits NMDAR current in hippocampal neurons by competing for the glycine-binding site" [1] and is also an essential amino acid. Oops.
[1] http://www.nature.com/mp/journal/v7/n4/full/4000976a.html
[1] http://www.nature.com/mp/journal/v7/n4/full/4000976a.html
Steve Jobs was know for eating fruit high in phenyalanine (well tyrosine)[1]. It may have contributed to his high performance.
[0] https://en.wikipedia.org/wiki/Phenylketonuria#Genetics [1] https://en.wikipedia.org/wiki/Tyrosine