Phenylalanine is the most commonly found aromatic, essential amino acid. In a normal individual it is converted to tyrosine, which in turn is used to synthesise dopamine and norepinephrine (nerurotransmitters). Phenylalanine takes three differnt forms; L-, D- and DL-. The L- form is the most common and the type in which it is incorporated into the body's proteins. The D- form acts as a painkiller and the DL- a combination of the two. Phenylalanine is used to elevate mood as it is involved with the nervous system, it can also aid memory and learning and can been used as an appetite suppressant. Treatment with phenylalanine can be benificial in sufferes of Parkinson's disease, to treat depression and the D form may also be helpful in the treatment of chronic pain in both osteo-arthritis and rheumatoid arthritis. Deficiency is rare but symptoms may include lethargy, edema, weakness, skin lesions as well as liver damage and slow growth.