Source:
Tyrosine is an important nonessential amino acid that is a precursor to a number of neurotransmitters that include L-dopa, dopamine, norepinephrine, and epinephrine. These neurotransmitters relate to our feeling of well being. Tyrosine is ynthesized in the body from phenylalanine and is found in soy products, chicken, turkey,  bananas, milk, cheese, yogurt, fish, peanuts, almonds, avocados, cottage cheese, lima beans, pumpkin seeds, and sesame seeds.

Physiology:
Tyrosine as a building block for several important brain chemicals i.e. epinephrine, norepinephrine, serotonin, and dopamine,  which all have an effect on regulating mood; therefore, deficiencies in tyrosine have been associated with depression. Tyrosine aids in the production of melanin, the pigment responsible for skin and hair color, and in the function of organs in the body responsible for making and regulating hormones, including the  thryroid, adrenal and pituitary glands. Tyrosine is also involved in the synthesis of enkephalins, substances that have pain-relieving effects in the body.

Clinical Studies:
Studies have shown Tyrosine to act as an antidepressant by increasing levels of norepinephrine as an adaptogen, as well as, improving learning and mental alertness. Tyrosine also supports the adrenal glands, helps alleviate stress, and increases dopamine levels. Gelenberg AJ, Gibson CJ, Wojcik JD. Neurotransmitter precursors for the treatment of depression. Psychopharmacol Bull 1982;18:7–18., Banderet LE, Lieberman HR. Treatment with tyrosine a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull 1989;22:759–62.

Modern day uses:
Today, Tyrosine is prescribed by physicians and herbal specialist for the following uses:

• Stress - secondary to its role as a precursor to norepinephrine and epinephrine, which are the two main stress related hormones, L-Tyrosine may also ease the adverse effects of psychosocial, environmental, and physical stress.
• Synthesis of a thyroid hormone - the amino acid also plays a role in the synthesis of a thyroid hormone Thyroxine, which participates in regulating the metabolic rate, healthy skin, mental health, and our growth rate.
• Antioxidant - because Tyrosine binds unstable molecules that can potentially cause damage to the cells and tissues, it is considered a mild antioxidant. Because of this, Tyrosine may be beneficial in heavy smokers and in individuals who have been exposed to radiation and/or harmful chemicals
• Melanin - L-tyrosine is converted by skin cells into melanin, the dark pigment that protects against the harmful effects of ultraviolet light.
• Enhanced libido - Besides being an effective source of quick energy for the brain, tyrosine converts to the amino acid L- Dopamine, which promotes sexual motivation and genital reflexes. Increased release of dopamine in sexual situations promotes sexual motivation, genital reflexes and copulation.
• Chronic fatigue and narcolepsy - (involuntary sleep) Tyrosine appears to have a mild stimulatory effect on the central nervous system.
• Drug detoxification - The amino acid appears to be a successful adjunct for the treatment of cocaine withdrawal. Tyrosine is often used in conjunction with
• Tryptophan and Imipramine (an antidepressant). Successful withdrawal from caffeine and nicotine has also been anecdotally reported.
• Enkephalins - substances that have pain-relieving effects in the body.

Precautions and/or adverse effects:
Individuals with preexisting medical conditions should consult with their physician particularly if they are taking prescription or over-the-counter-medications or supplements. Women who are pregnant or nursing and children should also consult with their physician prior to taking any new supplements. More specifically, individuals should avoid taking Tyrosine as a supplement if they have any of the following medical conditions:

• Hypertension
• Muscular Dystrophy
• Malignant Melanoma
• Hypothyroidism
• Glaucoma

or if they are taking any of the following medications:

• Monoamine Oxidase (MAO) inhibitors
• Tricyclic anti-depressants
• Serotonin re-uptake inhibitors (SSRIs) such as Prozac