Tyrosine is a nonessential amino acid. It is synthesized in the body from phenylalanine and is a precursor of adrenaline (epinephrine), norepinephrine, dopamine, thyroid hormones, and some types of estrogen. In order for tyrosine to metabolize into these substances, folic acid, niacin, vitamin C, and copper are needed. Low levels of tyrosine can lead to deficiencies in norepinephrine and dopamine—neurotransmitters that regulate mood. Depression can result. Animal studies have demonstrated that stressed animals have reduced levels of norepinephrine; however, administration of tyrosine prevented a norepinephrine deficiency. Tyrosine deficiency is also associated with low blood pressure, low body temperature, and restless leg syndrome.

Tyrosine aids in the the production of melanin (pigment responsible for hair and skin color) and in the functions of the adrenal, thyroid, and pituitary glands. A deficiency of tyrosine has been associated with hypothyroidism.

Because tyrosine binds unstable molecules that can potentially cause damage to the cells and tissues, it is considered a mild antioxidant. Thus, it may be useful in heavy smokers and in individuals exposed to chemicals and radiation.

Although tyrosine is found in soy products, chicken, fish, almonds, avocados, bananas, dairy products, lima beans, pumpkin seeds, and sesame seeds, it is difficult to get therapeutic amounts of it from food. It is also produced from phenylalanine in the body.

Many tyrosine supplements are available.

• Depression. Tyrosine appears to be a safe and effective treatment for depression; however, symptoms of depression recur when tyrosine is discontinued. Most data regarding tyrosine's efficacy in treating depression are anecdotal.
• Stress. Tyrosine seems to relieve the physical symptoms of stress if administered before the stressful situation, though limited human studies have been performed.
• Premenstrual syndrome (PMS). Though most data are anecdotal, tyrosine appears to help reduce the irritability, depression, and fatigue associated with PMS.
• Low sex drive. Tyrosine appears to stimulate the libido.
• Parkinson's disease. Parkinson's disease is treated with L-dopa, which is made from tyrosine; thus, the effects of tyrosine supplementation is being studied in Parkinson's disease patients.
• Weight loss. Tyrosine is an appetite suppressant and helps to reduce body fat.
• Chronic fatigue and narcolepsy. Tyrosine appears to have a mild stimulatory effect on the central nervous system.
• Drug detoxification. Tyrosine appears to be a successful adjunct for the treatment of cocaine abuse and withdrawal. It is often used in conjunction with tryptophan and imipramine (an antidepressant). In one study, 75% to 80% of patients treated with tyrosine stopped cocaine use completely or decreased usage by 50%. Successful withdrawal from caffeine and nicotine has also been anecdotally reported.
• Phenylketonuria (PKU). Tyrosine supplementation is advocated in patients with PKU; however, it is necessary to control plasma tyrosine levels (normal: 45 mcmol/L) before tyrosine supplementation is considered.

• For depression, premenstrual syndrome, and chronic fatigue, a 500 to 1,000 mg dose before each of three meals is recommended.
• For stress, 1,500 mg/day is recommended.
• For low sex drive, Parkinson's disease, drug detoxification, and weight loss, 1 to 2 g/day in divided doses is recommended.
• It appears that up to 12 g/day of tyrosine can be ingested safely. However, high-dose therapy should be monitored by a health care provider.

• Migraine headache
• High blood pressure
• Mild gastric upset
• Promotes cancer cell division

Tyrosine should not be given to patients who are taking monoamine oxidase (MAO) inhibitors for depression or to patients with high blood pressure because it can cause dangerously high blood pressure elevations. Tyrosine may also promote the growth of malignant melanoma by promoting the division of cancer cells.

Amino acids should not be taken regularly; ingestion may inhibit the body's natural production of these chemicals.

L-tyrosine (200 and 400 mg/kg) significantly potentiated the anorexigenic effects of phenylpropanolamine (5, 10, or 20 mg/kg), ephedrine (5, 10, or 20 mg/kg), and amphetamine (0.75, 1.25, or 1.75 mg/kg) in a dose-dependent manner in rats (Hull and Maher 1990). More research is needed to determine whether L-tyrosine supplementation would produce similar results in humans.

Levodopa (L-dopa) may decrease tyrosine and tryptophan levels (Riederer 1980). However, administering L-dopa with tyrosine may decrease absorption of the amino acid by competitively inhibiting the transport system (Awad 1984).

L-tyrosine increased morphine-induced analgesia 154% in mice; only the L-form of tyrosine produced these effects (Hull et al. 1994). Further studies are needed to determine whether L-tyrosine would potentiate the analgesic activity of morphine in humans.

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