L-tyrosine is an essential amino acid, important for the structure of almost all proteins in the body, which the body synthesizes from phenylalanine (another amino acid).    It participates in the synthesis of thyroid hormones (Thyroxine T4 and Triiodothyronine T3) and gives very good results in cases of hypothyroidism.    It is also the precursor in the production of many neurotransmitters, including L-dopa, dopamine, norepinephrine and epinephrine.    L-Tyrosine, through its effect on neurotransmitters, can affect various health conditions in the body, including Parkinson's disease, depression and other disorders.