phenylalanine      C₉H₁₁O₂N       

 One of the amino acids which the body cannot manufacture itself, but must acquire from food. It is abundant in meats and cheese. 

Phenylalanine is a precursor of tyrosine and together they lead to the formation of thyroxine or thyroid hormone and of adrenaline and noradrenaline which is converted into a neurotransmitter, a brain chemical which transmits nerve impulses. This neurotransmitter is used by the brain to manufacture noradrenaline which promotes mental alertness, memory, elevates mood and suppresses the appetite very effectively. 

Along with another amino acid, tryptophan, phenylalanine governs the release of an intestinal hormone called cholecystokinin. 

Overuse of phenylalanine supplements can cause anxiety, headaches and hypertension and are contraindicated for pregnant woman, those who suffer from anxiety attacks, high blood pressure, PKU, pigmented melanoma or anyone taking an anti-depressant containing monoamine oxidase inhibitors.
Source: OMD