What does it do? L-tyrosine is a nonessential amino acid (protein building block) that the body synthesizes from phenylalanine, another amino acid. Tyrosine is important to the structure of almost all proteins in the body. It is also the precursor of several neurotransmitters, including L-dopa, dopamine, norepinephrine, and epinephrine. L-tyrosine, through its effect on neurotransmitters, may affect several health conditions, including Parkinson’s disease, depression, and other mood disorders. Studies have suggested that tyrosine may help people with depression.1 Preliminary findings indicate a beneficial effect of tyrosine, along with other amino acids, in people affected by dementia, including Alzheimer’s disease.2 Due to its role as a precursor to norepinephrine and epinephrine (two of the body’s main stress-related hormones) tyrosine may also ease the adverse effects of environmental, psychosocial, and physical stress.3 4 5 6 7 8 9
L-tyrosine is converted by skin cells into melanin, the dark pigment that protects against the harmful effects of ultraviolet light. Thyroid hormones, which have a role in almost every process in the body, also contain tyrosine as part of their structure.
People born with the genetic condition phenylketonuria (PKU) are unable to metabolize the amino acid phenylalanine. Mental retardation and other severe disabilities can result. While dietary phenylalanine restriction prevents these problems, it also leads to low tyrosine levels in many (but not all) people with PKU. Tyrosine supplementation may be beneficial in some people with PKU, though the evidence is conflicting.10
L-tyrosine has been used in connection with the following conditions (refer to the individual health concern for complete information):
Phenylketonuria (for deficiency)
and relatively consistent scientific data showing a substantial health benefit.
Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
An herb is primarily supported by traditional use, or the herb or supplement has little scientific support and/or minimal health benefit.
Who is likely to be deficient? Some people affected by PKU are deficient in tyrosine. Tyrosine levels are occasionally low in depressed people.11 Any person losing large amounts of protein, such as those with some kidney diseases, may be deficient in several amino acids, including tyrosine.12
How much is usually taken? Most people should not supplement with L-tyrosine. Some human research with people suffering from a variety of conditions used 100 mg per 2.2 pounds of body weight, equivalent to about 7 grams per day for an average-sized person. The appropriate amount to use in people with PKU is not known, therefore, the monitoring of blood levels by a physician is recommended.
Are there any side effects or interactions? L-tyrosine has not been reported to cause any serious side effects. However, it is not known whether long-term use of L-tyrosine, particularly in large amounts (such as more than 1,000 mg per day) is safe. For that reason, long-term use of L-tyrosine should be monitored by a doctor.
Are there any drug interactions? Certain medications may interact with L-tyrosine. Refer to the drug interactions safety check for a list of those medications.
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2. Meyer JS, Welch KMA, Deshmuckh VD, et al. Neurotransmitter precursor amino acids in the treatment of multi-infarct dementia and Alzheimer’s disease. J Am Geriatr Soc 1977;7:289–98.
3. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull 1989;22:759–62.
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11. Chiaroni P, Azorin JM, Bovier P, et al. A multivariate analysis of red blood cell membrane transports and plasma levels of L-tyrosine and L-tryptophan in depressed patients before treatment and after clinical improvement. Neuropsychobiology 1990;23:1–7.
12. Alvestrand A, Ahlberg M, Forst P, Bergstrom J. Clinical results of long-term treatment with a low protein diet and a new amino acid preparation in patients with chronic uremia. Clin Nephrol 1983;19:67–73.