Tyrosine

Scientific Name(s): 4-hydroxyphenylalanine, C9H11NO3
Common Name(s): L-tyrosine, Tyrosine

Medically reviewed by Drugs.com. Last updated on Nov 10, 2022.

Clinical Overview

Use

There is no evidence to support the use of tyrosine in the metabolic genetic disorder phenylketonuria. Some evidence for improved cognitive performance in conditions of stress, including sleep deprivation, exists. Clinical trial data for other conditions is limited and does not support tyrosine supplementation, including for the enhancement of sports performance.

Dosing

Limited clinical studies use 100 to 150 mg/kg per day. Manufacturers commonly recommend 500 to 1,500 mg/day, and dosages of more than 12 g/day are not recommended.

Contraindications

Tyrosine is contraindicated in hyperthyroidism or Graves disease because it may increase levels of thyroid hormone. Coadministration of tyrosine with monoamine oxidase inhibitors (MAOIs) is contraindicated.

Pregnancy/Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

Coadministration of tyrosine and monoamine oxidase inhibitors (MAOIs) is contraindicated.

Adverse Reactions

Information is limited. Tyrosine supplementation may trigger migraine.

Toxicology

Information is limited.

Source

Tyrosine is made endogenously from phenylalanine and can be found in soy products, milk, cheese, yogurt, chicken, turkey, fish, peanuts, almonds, bananas, lima beans, avocado, pumpkin seeds, and sesame seeds.Zimmermann 2001

History

The name tyrosine is derived from the Greek tyri, meaning "cheese." Tyrosine was first identified in cheese protein casein in 1846 by German chemist Justus von Liebig.

Chemistry

Tyrosine is a nonessential, yet indispensable, amino acid made endogenously and eaten in a usual diet. It is a fundamental building block for proteins, specifically for neurotransmitters. Tyrosine is converted to L-dopa, dopamine, epinephrine, norepinephrine, triiodothyronine (T3), thyroxine (T4), and melanin.

Uses and Pharmacology

Anorexia nervosa

Clinical data

The safety and pharmacokinetics of tyrosine loading in 2 adolescents diagnosed with anorexia nervosa was compared to that of 2 healthy controls. Supplementation with L-tyrosine 2.5 g twice daily for 12 weeks resulted in percent expected body weight being relatively "weight-restored" in Patient 2 (96%; actual body mass index [BMI] by 50^th Centile BMI on growth charts) and essentially unchanged in Patient 1 (80%). No side effects were observed. Single-dose pharmacokinetics in the 2 healthy controls revealed a percentage change in tyrosine levels that ranged from 152% to 194%, with Patient 2 experiencing a similar change (164%) and Patient 1 exhibiting a much higher tyrosine peak response (300% change). Overall, tyrosine levels peaked at 2 to 3 hours (132 to 240 mcmol/L) and approached baseline at 8 hours (62 to 100 mcmol/L).(Hart 2021)

Core temperature

Clinical data

L-tyrosine administration has been shown to increase the cutaneous vasoconstrictive response during cold exposure in older adults, thereby minimizing heat loss. Additionally, it enhances cognitive and psychomotor performance in young adults during cold stress. To further explore thermoregulatory effects of L-tyrosine during cooling, 18 healthy participants were enrolled in a double-blind, randomized, placebo-controlled crossover study. The participants comprised 9 young (mean age, 25 years) and 9 older adults (mean age, 72 years). Single-dose tyrosine led to a significant improvement in the ability of older adults to regulate their core temperature and significantly reduced the core temperature decline during whole-body cooling (P<0.05). However, it had no effect on thermoregulatory variables in young adults. Although tyrosine reduced the perception of cold in young adults compared to placebo (P=0.007), no significant differences were found between tyrosine or placebo in discomfort or cold perception in older versus younger adults. Tyrosine augmented the reflex cutaneous vasoconstrictive response in the older adults (P<0.05) to that similar of the young adults, but did not affect the response in the younger adults.(Lang 2020)

Depression

Clinical data

Despite a theoretical basis for the use of tyrosine in depression, studies conducted in the 1980s using small sample sizes did not show any benefit.(Meyers 2000, Parker 2011) More recent studies focused on serotonin precursors, revealing little evidence of a place in therapy for tyrosine.(Meyers 2000, Parker 2011, Fernstrom 2000)

Exercise/Performance

Clinical data

Limited clinical studies provide equivocal data on the effects of supplemental tyrosine in exercise,(Chinevere 2002, Tumilty 2011) with older studies conducted in the 1980s reporting more positive findings. Among 8 cyclists exercising in heat, tyrosine 150 mg/kg appeared to improve endurance,(Tumilty 2011) while a similar trial also conducted among cyclists resulted in increased plasma tyrosine levels but not improved performance; however, tyrosine may have altered their perception of fatigue.(Chinevere 2002)

The effect of tyrosine on core cognitive-control performance, as measured by stopping overt responses, was investigated in a small double-blind, randomized, placebo-controlled cross-over study in 22 young healthy female adults. One hour after administration of L-tyrosine 2 g (in 400 mL orange juice), participants were observed to more efficiently inhibit unwanted actions compared to the placebo phase (P<0.05). Response execution was not affected and no significant changes were found in physiological parameters (eg, blood pressure, heart rate) or mood.(Colzato 2014)

Fear expression

Clinical data

In a double-blind, randomized, placebo-controlled study of university students (N=46), administration of a single-dose of L-tyrosine 2 g 1 hour before fear conditioning significantly inhibited the magnitude of fear response compared to placebo (P=0.006) based on skin conductance responses. Results of a visual analog scale (VAS) questionnaire before and after drug administration but before fear conditioning confirmed no effect on mood scores. These results demonstrate the effect of the catecholamine precursor, L-tyrosine, in being able to augment dopamine and norepinephrine levels and mitigate fear expression without affecting measures of mood or alertness.(Soranzo 2019)

Parkinson disease

Animal data

Limited studies with animal models of Parkinson disease provide little evidence of supplemental tyrosine effect.(Fernstrom 2000, Feve 2012)

Clinical data

Tyrosine hydroxylase is the rate-limiting step in the production of L-dopa and dopamine, forming the basis for the use of supplemental tyrosine. However, clinical trial data supporting a place in therapy are lacking.(Fernstrom 2000, Feve 2012)

Phenylketonuria

Tyrosine deficiency is rare, but possible among people with phenylketonuria because of their avoidance of phenylalanine-containing foods such as milk, eggs, and meat. Tyrosinemia is also rare.(Glaeser 1979)

Clinical data

A Cochrane meta-analysis of 6 trials with a total of 56 patients found that increased blood tyrosine levels result from supplementation. However, this does not translate to improvement in any outcome measures, including intelligence, neurophysiological performance, growth, nutritional status, quality of life, or mortality.(Posner 2009) A case study suggests a role for tyrosine supplementation in patients with attention deficit hyperactivity disorder symptoms who also have phenylketonuria.(Webster 2013)

Stress

Animal data

Research reveals no recent animal data regarding the use of supplemental tyrosine for the use of stress prevention. Tyrosine has been shown to impair enzymes of energy metabolism in the cerebral cortex of rats, but the implications of this finding are unclear.(de Andrade 2012)

Clinical data

Studies evaluating supplemental tyrosine's role in mitigating the effects of stress on cognitive performance and memory deficit have generally found positive, but limited, effects (and lesser than for amphetamine).(Deijen 1999, Fernstrom 2000) Among military cadets (N = 21), cognitive performance was supported by tyrosine 10 g/day during physical and psychological training.(Deijen 1999) Tyrosine 300 mg/kg in 2 divided doses mitigated the stress-related decrease in cognitive performance induced by cold immersion in another small study.(Mahoney 2007) Following sleep deprivation, tyrosine 150 mg/kg improved some aspects of cognitive and motor performance in another small study.(Magill 2003) At a dose of 100 mg/kg, L-tyrosine administered 90 minutes prior to heat exposure (45°C x 90 minutes) in 10 healthy young males from the Indian military mitigated the reduction in information processing and cognitive decline seen during the placebo phase of a double-blind, randomized, cross-over study. Tyrosine was also observed to increase plasma norepinephrine levels compared to placebo.(Kishore 2013)

Dosing

Tyrosine is unable to cross the blood-brain barrier, despite brain tyrosine levels being dependent on plasma concentrations.Glaeser 1979 An alternative form, N-alpha-linolenoyl tyrosine, has been developed to overcome this issue.Yehuda 2002 Coadministration of tyrosine with vitamin B6, folate, and copper could enhance conversion of tyrosine to brain neurotransmitters.

Limited clinical studies use 100 to 150 mg/kg per day. A single dose of 2 g has been used in a cognitive performance trial.Colzato 2014, Kishore 2013, Magill 2003, Mahoney 2007, Tumilty 2011

Manufacturers commonly recommend 500 to 1,500 mg/day, and dosages of more than 12 g/day are not recommended.

Pregnancy / Lactation

Information regarding safety and efficacy in pregnancy and lactation is lacking.

Interactions

Case reports are lacking; however, tyrosine is contraindicated in patients taking MAOIs, including isocarboxazid, phenelzine, tranylcypromine, and selegiline.

Monoamine oxidase inhibitors: Tyrosine may enhance the hypertensive effect of MAOIs. Avoid combination.(Marplan November 2018, Nardil September 2009)

Adverse Reactions

Case reports are lacking; however, higher plasma tyrosine levels have been noted in cases of chronic migraine.D'Andrea 2013

Toxicology

Symptoms associated with hereditary tyrosinemia, including the development of skin and eye lesions, were apparent at plasma levels 10 times of that found following administration of tyrosine 150 mg/kg in clinical trials.Glaeser 1979 L-tyrosine has been safely used as an adjuvant in vaccine preparation.Baldrick 2002

References

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This information relates to an herbal, vitamin, mineral or other dietary supplement. This product has not been reviewed by the FDA to determine whether it is safe or effective and is not subject to the quality standards and safety information collection standards that are applicable to most prescription drugs. This information should not be used to decide whether or not to take this product. This information does not endorse this product as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this product. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this product. This information is not specific medical advice and does not replace information you receive from your health care provider. You should talk with your health care provider for complete information about the risks and benefits of using this product.

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