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 function of organs in the body responsible for making and regulating hormones, including the adrenal, thryroid, and pituitary glands. Tyrosine is also involved in the synthesis of enkephalins, 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.