Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2 Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
150 mg for every 2.2 lbs (1 kg) of body weight, split into two doses taken before stressful activitiy (take the second dose 40 to 90 minutes after the first)
Occasionally taking this amino acid before a stressful activity may help maintain your mental capacity.
Tyrosine is an amino acid used by the body to produce certain adrenal stress hormones and chemical messengers in the nervous system (neurotransmitters). Animal research shows that brain levels of these substances decline with stress, and that giving animals tyrosine supplements reverses this decline and improves various tests of performance in stressed animals.1 In a controlled study, a protein drink containing 10 grams per day of tyrosine was more effective than a carbohydrate drink for improving mental performance scores in a group of cadets taking a stressful six-day combat training course.2 A double-blind trial in humans found that one-time administration of 150 mg of tyrosine per 2.2 pounds of body weight helped prevent a decline in mental performance for about three hours during a night of sleep deprivation.3 Single administrations of tyrosine (100 to 150 mg per 2.2 pounds of body weight) have also helped preserve mental performance during physically stressful conditions such as noise or extreme cold in several controlled studies.4 , 5 , 6 , 7
Consult your doctor
Some people with depression have been found to improve with tyrosine.
The amino acid L-tyrosine can be converted into norepinephrine, a neurotransmitter that affects mood. Women taking oral contraceptives have lower levels of tyrosine, and some researchers think this might be related to depression caused by birth control pills.8 L-tyrosine metabolism may also be abnormal in other depressed people9 and preliminary research suggests supplementation might help.10 , 11 Several doctors recommend a 12-week trial of L-tyrosine supplementation for people who are depressed. Published research has used a very high amount—100 mg per 2.2 pounds of body weight (or about 7 grams per day for an average adult). It is not known whether such high amounts are necessary to produce an antidepressant effect.
Consult a qualified healthcare practitioner
Supplementing with L-Tyrosine may help prevent a deficiency caused by the PKU diet and improve behavoir.
PKU results from a deficiency or malfunction of the enzyme, phenylalanine hydroxylase, which converts phenylalanine to . People with PKU have elevated concentrations of phenylalanine and low levels of L-tyrosine, which may contribute to behavior problems. In addition, low L-tyrosine levels in women with PKU may contribute to fetal damage. In some, but not all, double-blind studies, keeping L-tyrosine levels in the normal range by adding supplemental L-tyrosine to the diet improved behavior. In a preliminary study, blood L-tyrosine levels fluctuated significantly in people with PKU, suggesting a need for careful laboratory monitoring of people supplementing with L-tyrosine.
Alcohol Withdrawal (Glutamine, Multivitamin, Phenylalanine, Tryptophan)
Refer to label instructions
In double-blind research, alcoholics treated with L-tyrosine combined with DLPA (D,L-phenylalanine), L-glutamine, prescription L-tryptophan, plus a multivitamin had reduced withdrawal symptoms and decreased stress.
Kenneth Blum and researchers at the University of Texas have examined neurotransmitter deficiencies in alcoholics. Neurotransmitters are the chemicals the body makes to allow nerve cells to pass messages (of pain, touch, thought, etc.) from cell to cell. Amino acids are the precursors of these neurotransmitters. In double-blind research, a group of alcoholics were treated with 1.5 grams of D,L-phenylalanine (DLPA), 900 mg of L-tyrosine, 300 mg of L-glutamine, and 400 mg of L-tryptophan (now available only by prescription) per day, plus a multivitamin-mineral supplement.12 This nutritional supplement regimen led to a significant reduction in withdrawal symptoms and decreased stress in alcoholics compared to the effects of placebo.
Refer to label instructions
L-tyrosine is the direct precursor to L-dopa and therefore could be an alternative to L-dopa therapy, however, it should not be taken with L-dopa as it may interfere with L-dopa transport to the brain.
L-tyrosine is the direct precursor to L-dopa. Theoretically, supplementing L-tyrosine could be an alternative to L-dopa therapy; however, L-tyrosine should not be taken with L-dopa as it may interfere with the transport of L-dopa to the brain.13 One small preliminary trial demonstrated that some people with Parkinson’s disease who supplemented with L-tyrosine (45 mg per pound of body weight) for three years had better clinical results and fewer side effects than did patients using L-dopa.14 Until these findings are confirmed, L-tyrosine should not be used as a replacement for, or in addition to, L-dopa.
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.
Dairy products, meats, fish, wheat, oats, and most other protein-containing foods contain tyrosine.
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.
1. Owasoyo JO, Neri DF, Lamberth JG. Tyrosine and its potential use as a countermeasure to performance decrement in military sustained operations. Aviat Space Environ Med 1992;63:364–9 [review].
2. Deijen JB, Wientjes CJ, Vullinghs HF, et al. Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course. Brain Res Bull1999;48:203–9.
3. Neri DF, Wiegmann D, Stanny RR, et al. The effects of tyrosine on cognitive performance during extended wakefulness. Aviat Space Environ Med 1995;66:313–9.
4. Banderet LE, Lieberman HR. Treatment with tyrosine, a neurotransmitter precursor, reduces environmental stress in humans. Brain Res Bull 1989;22:759–62.
5. Shurtleff D, Thomas JR, Schrot J, et al. Tyrosine reverses a cold-induced working memory deficit in humans. Pharmacol Biochem Behav 1994;47:935–41.
6. Deijen JB, Orlebeke JF. Effect of tyrosine on cognitive function and blood pressure under stress. Brain Res Bull 1994;33:319–23.
7. Dollins AB, Krock LP, Storm WF, et al. L-tyrosine ameliorates some effects of lower body negative pressure stress. Physiol Behav 1995;57:223–30.
8. Rose DP, Cramp DG. Reduction of plasma tyrosine by oral contraceptives and oestrogens: a possible consequence of tyrosine aminotransferase induction. Clin Chim Acta 1970;29:49–53.
9. Moller SE. Tryptophan and tyrosine availability and oral contraceptives. Lancet 1979;2:472 [letter].
10. Kishimoto H, Hama Y. The level and diurnal rhythm of plasma tryptophan and tyrosine in manic-depressive patients. Yokohama Med Bull 1976;27:89–97.
11. Gelenberg AJ, Wojcik JD, Growdon JH, et al. Tyrosine for the treatment of depression. Am J Psychiatry 1980;137:622–3.
12. Blum K. A commentary on neurotransmitter restoration as a common mode of treatment for alcohol, cocaine and opiate abuse. Integr Psychiatr 1986;6:199–204.
13. Wurtman RJ, Wurtman JJ, eds. Nutrition and the Brain, vol 7. New York: Raven Press, 1986.
14. Lemoine P, Robelin N, Sebert P, Mouret J. L-tyrosine: a long term treatment of Parkinson’s disease. C R Acad Sci III 1989;309:43–7.
15. 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.
16. 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.
Last Review: 05-01-2013
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2014.
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