Tyrosine is a nonessential protein amino acid that is critical for the structural integrity of nearly all proteins found in the body. It is synthesized from the essential amino acid phenylalanine, and may be conditionally essential in times of prolonged stress or severe conditions. Tyrosine is a direct precursor to the catecholamines epinephrine, norepinephrine, dopamine, and serotonin. These neurotransmitters are vital in processes relating to the regulation of mood, stress response, and mental functioning.

Tyrosine also aids in the function and maintenance of organs responsible for the production of specialized hormones. The adrenal, thyroid, and pituitary glands are all dependant upon sufficient levels of tyrosine to create hormones that regulate various metabolic and neurological processes within the body. Tyrosine is also required to form melanin, the dark pigment responsible for hair and skin color. This pigment is critical as it also provides protection from the harmful effects of ultraviolet light (UV exposure).

This unique nonessential amino acid may also afford the body with mild antioxidant properties. Tyrosine binds many unstable molecules that may potentially cause damage to certain cellular and tissue structures (free radicals). Supplemental tyrosine, consequently, may be beneficial for individuals suffering from the exposure to toxic chemicals often found in the pollution resulting from smoking and radiation.