Popular with weightlifters and other exercise buffs, Tyrosine, or L-Tyrosine, is a nonessential amino acid and is a building block of protein. Tyrosine, or L-Tyrosine, is believed to be a precursor of dopamine and adrenal hormones. Tyrosine, or L-Tyrosine, can be obtained from meat, seafood, and wheat products. Tyrosine, or L-Tyrosine, is used by athletes to offset the effects of overtraining and fatigue. Tyrosine, or L-Tyrosine, is also thought to increase mental alertness and help those who are trying to lose weight.

Tyrosine is a conditionally essential amino acid which works in the presence of ascorbic acid (vitamin C). Tyrosine is a nutritional co-precursor of thyroid hormones and some neurochemicals called catecholamines which are natural hormonal substances that act as extra cellular messengers between the brain, central nervous tissue and endocrine system. Tyrosine, indirectly, is an all-natural nutritional precursor to dopa, dopamine, norepinephrine (noradrenaline) and epinephrine (adrenaline). Tyrosine is known to be a necessary constituent of normal brain function but can be synthesized from phenylalanine.Tyrosine has been found to be useful in some researched cases of depression which are not especially amenable to treatment with tryptophan or tryptophan inducing formulas.

Tyrosine readily passes through the brain-blood barrier, reacting positively with the BCAA's (branched chain amino acids).It is thought to be primarily concentrated in brain tubulin, an intracellular protein that is important for the formation, structure and integrity of neurons and neural pathways, the important message sending "devices" of the brain. Nutritional Caution: It should be noted that the new artificial sweetener aspartame, which contains phenylalanine (a precursor to tyrosine), increases brain tyrosine; this may have some beneficial effects on those suffering from depression, but may worsen those who are manic- or schizophrenic-inclined. Tyrosine is also found in high concentration within muscle tissue.