It is a precursor of the important brain neurotransmitters epinephrine, norepinephrine and dopamine, which transmit nerve impulses and are essential to prevent depression.
Dopamine is vital to mental function and seems to play a role in sex drive.
Tyrosine is also used by the thyroid gland to produce one of the major hormones, Thyroxin. This hormone regulates growth rate, metabolic rate, skin health and mental health. It is used in the treatment of anxiety, depression, allergies and headaches. Animals subjected to stress in the laboratory have been found to have reduced levels of the brain neurotransmitter norepinephrine. Doses of tyrosine prior to stressing the animals prevents reduction of norepinephrine.