Tyrosine is a nonessential amino acid that is synthesized in the body from phenylalanine. As a building block for several important brain chemicals, tyrosine is needed to make epinephrine, norepinephrine, serotonin, and dopamine, all of which work to regulate mood. Deficiencies in tyrosine, therefore, have been associated with depression. Tyrosine also aids in the production of melanin (pigment responsible for hair and skin color) and in the function of organs in the body responsible for making and regulating hormones, including the adrenal, thyrroid, and pituitary glands. Tyrosine is also involved in the synthesis of eukephalins, substances that have pain-relieving effects in the body.

Low levels of tyrosine have been associated with low blood pressure, low body temperature, and an under active thyroid. This does not mean, however, that taking tyrosine supplements will avoid these particular circumstances.

Because tyrosine binds unstable molecules (called free radicals) that can potentially cause damage to the cells and tissues, it is considered a mild antioxidant. Thus, tyrosine may be useful for people who have been exposed to harmful chemicals (such as from smoking) and radiation.