Tyrosine was first isolated from casein in 1849 and is abundant in insulin as well as the enzyme papain and can be synthesized from the amino acid phenylalanine in the body.

Tyrosine is an nonessential amino acid, a precursor for L-dopa, norepinephrine, epinephrine, and dopamine. Tyrosine is vital to mental function and enhances the sex drive. It is used to produce thyroxin which regulates growth, metabolism, skin, and mental health.

Tyrosine is metabolically synthesized from phenylalanine to become the para-hydroxy derivative of that important amino acid. This hydroxylated amino acid participates in the synthesis of many important biochemicals including the thyroid hormones, the melanin biological pigments, and the catecholamines, an important class of biological regulators. Tyrosine is incorporated into proteins and enzymes at the molar rate of 3.5 percent with respect to the other amino acids.

It is a precursor of the neurotransmitters epinephrine, norepinephrine and dopamine, all of them extremely important in the brain and transmits nerve impulses, and prevents depression. Dopamine is also vital to mental function and seems to play a role in sex drive.

The action of this amino acid in brain functions is clear with its link to dopamine as well as norepinephrine. It is also helpful in suppressing the appetite and reducing body fat, production of skin and hair pigment, the proper functioning of the thyroid, as well as the pituitary and adrenal gland. It is used for stress reduction and may be beneficial in narcolepsy, fatigue, anxiety, depression, allergies, headaches, as well as drug withdrawal. In a study using soldiers, tyrosine proved effective in alleviating stress and keeping them more alert.

Tyrosine, a parent amino acid for skin, hair, and eye pigments, is involved in syndromes, known generally as oculocutaneous albinism, that are characterized by the failure to form melanin pigments, resulting in partial or complete albinism. It is also the precursor amino acid for the thyroid gland hormone thyroxin, and a defect in this may result in hypothyroidism - an enlargement of the thyroid gland (goiter), severe growth failure, and retardation of central nervous system development. A deficiency may also have symptoms of low blood pressure, low body temperature (including cold hands and feet) and "restless leg syndrome."

Tyrosine and tryptophan have with been used with some success in the treatment of cocaine abuse and in another study it was combined with the antidepressant Imipramine to treat chronic cocaine abuse where it was reported that the combination blocked the cocaine high and prevented the severe depression that accompanies withdrawal.

Meat, dairy products, eggs, as well as almonds, avocados and bananas are good sources of this nutrient.