Phenylalanine (Phe; F) is an essential amino acid. The body converts phenylalanine into tyrosine which is a non-essential amino acid and is involved in the production of the neurotransmitters norepinephrine (noradrenaline), dopamine, and epinephrine (andrenalin). Tyrosine is also needed for the synthesis of thyroid hormone and the  skin pigment melanin.