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L-tyrosine

Conditionally essential amino acid, precursor of catecholamines and thyroid hormones

ATC code: A16AA-L-TYROSINE

Brand names – supplements: Jarrow Formulas L-Tyrosine, NOW Foods L-Tyrosine, Solgar L-Tyrosine, Doctor's Best L-TyrosineSupplements are not tested in clinical trials and are not registered as medications.

Updated · Methodology

Indications

B

Phenylketonuria

Adjunct

In patients with phenylketonuria the endogenous synthesis of tyrosine from phenylalanine is impaired by phenylalanine hydroxylase deficiency. The strict low-protein diet causes secondary tyrosine deficiency, replaced through specialised amino acid formulas. The 2017 European PKU guidelines (van Wegberg et al.) include tyrosine in replacement therapy. A Cochrane systematic review found no significant benefit of separate L-tyrosine supplementation beyond the diet on neuropsychological outcomes. Self-administered L-tyrosine in PKU does not substitute the prescribed dietary formulas; the metabolic centre team sets the regimen and doses.

Sources

  1. European PKU guidelines (van Wegberg et al.): Key European guidelines for the diagnosis and management of patients with phenylketonuria (2017)
  2. Cochrane Database of Systematic Reviews: Tyrosine supplementation for phenylketonuria (2021)
  3. Orphanet Journal of Rare Diseases: The complete European guidelines on phenylketonuria: diagnosis and treatment (2017)

ICD-10: E70.0 · ICD-11: 5C50.0

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

D

Cognitive performance under acute stress

Not recommended

L-tyrosine is marketed as a supplement that supports memory and attention under sleep deprivation and stress. The evidence base is limited to military studies: Deijen and colleagues in 1999 showed cognitive test improvement in cadets after a week of intense training on 2 g/day. Civilian RCTs failed to reproduce the effect reliably, with small short trials. did not confirm in 2011 the health claim that tyrosine contributes to catecholamine synthesis and performance. If memory and concentration trouble the patient, start with sleep hygiene, ferritin, B12 and thyroid hormone checks, discuss the request with a doctor and consider a second opinion before taking tyrosine on your own.

Sources

  1. Brain Research Bulletin: Tyrosine improves cognitive performance and reduces blood pressure in cadets after one week of a combat training course (1999)
  2. EFSA: Scientific Opinion on the substantiation of health claims related to L-tyrosine and contribution to normal synthesis of catecholamines (2011)
D

Major depressive disorder

Not recommended

L-tyrosine is marketed as a natural precursor of dopamine and noradrenaline that supports mood in depression. Direct testing does not back this up: in a double-blind trial of 65 patients with major depression, tyrosine at 100 mg/kg per day for 4 weeks did not beat placebo and showed no antidepressant activity (Gelenberg, 1990). Reviews by Parker and Brotchie (2011) and Jongkees (2015) confirm the lack of benefit in depression and limit tyrosine's effect to short-term attention under acute stress or sleep loss. The European Food Safety Authority () did not accept health claims linking L-tyrosine to attention. Tyrosine is absent from depression treatment recommendations and has no proven benefit, though no harm at usual doses is documented either.

Sources

  1. EFSA Journal: Scientific Opinion on the substantiation of health claims related to L-tyrosine and contribution to normal synthesis of catecholamines (ID 1928), increased attention (ID 440, 1672, 1930), and contribution to normal muscle function (ID 1929) pursuant (2011)
  2. Journal of Psychiatric Research: Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands - A review (2015)
  3. Acta Psychiatrica Scandinavica: Mood effects of the amino acids tryptophan and tyrosine: 'Food for Thought' III (2011)
  4. Journal of Affective Disorders: Tyrosine for depression: a double-blind trial (1990)

ICD-10: F32.9 · ICD-11: 6A70.Z

F

Hypothyroidism and thyroid support

Not recommended

L-tyrosine is marketed as a thyroid hormone precursor and a way to support the thyroid, often paired with iodine. Tyrosine is a building block of thyroxine, but the body's stores of it do not limit hormone synthesis, and no clinical trials show that tyrosine supplements improve thyroid function. In hypothyroidism, tyrosine does not replace levothyroxine, the first-line treatment recommended by the American Thyroid Association and Spanish endocrinologists (SEEN); choosing a supplement over levothyroxine leaves an underactive thyroid untreated. The common tyrosine plus high-dose iodine combination adds a separate risk, because excess iodine can trigger thyroid dysfunction, especially in people with autoimmune (Hashimoto) thyroiditis, the most frequent cause of hypothyroidism. Tyrosine is therefore not recommended for thyroid support or for treating hypothyroidism.

Sources

  1. Thyroid: Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement (2014)
  2. Endocrine Reviews: Risks of Iodine Excess (2024)
  3. Endocrinology and Metabolism (Seoul): Effects of Increased Iodine Intake on Thyroid Disorders (2014)

ICD-10: E03.9 · ICD-11: 5A00

How to read tiers A–F
  • AStrong evidence – first or second line in international guidelines
  • BRecommended in selected cases
  • CStudy data contradict each other
  • DBenefit not proven, no documented harm
  • FDocumented harm, or risk without benefit

Mechanism of action

Conditionally essential amino acid. The body synthesises tyrosine from phenylalanine via phenylalanine hydroxylase; in phenylketonuria this pathway is blocked, so tyrosine becomes essential for these patients. Tyrosine is a direct precursor of dopamine, noradrenaline and adrenaline, plus thyroid hormones T3 and T4. This is the basis for the hypothesis that supplementation may transiently support catecholamine synthesis under acute stress and offset neurotransmitter depletion. Clinical data in civilian patients are limited.

Safety

Contraindications

  • Hypersensitivity to tyrosine
  • Hyperthyroidism and thyrotoxicosis
  • Non-selective MAO inhibitors
  • Melanoma (theoretical risk of tyrosinase stimulation)
  • Phaeochromocytoma

Serious adverse effects

  • Hypertensive crisis when combined with non-selective MAO inhibitors
  • Worsening of thyrotoxicosis
  • Allergic reactions

Common adverse effects

  • Nausea and abdominal pain
  • Headache
  • Insomnia when taken in the afternoon or evening
  • Palpitations

Pregnancy: can you take L-tyrosine?

Safe in food-derived amounts. Safety of pharmacological doses above 1 g/day in pregnancy has not been studied. In PKU the metabolic centre sets the dose and composition of replacement therapy.

Breastfeeding: can you take L-tyrosine?

Compatible. Tyrosine is naturally present in human milk and dietary protein. Supplemental doses do not cause clinically significant infant exposure.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Label mentions1 mention

Verbatim lines from the interaction sections, in the language of the label

From other drugs’ labels

  • CriticalPhenelzine
    «CONTRAINDICATIONS: The potentiation of sympathomimetic substances and related compounds by MAO inhibitors may result in hypertensive crises (see WARNINGS ). Therefore, patients being treated with…»

    FDA, section 4 · Open on DailyMed

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Frequently asked

What is L-tyrosine used for?

L-tyrosine is evaluated for the following indications with varying evidence strength: Phenylketonuria (evidence tier B), Cognitive performance under acute stress (evidence tier D), Major depressive disorder (evidence tier D). See the full indication matrix with dosing and citations above on this page.

What are the side effects of L-tyrosine?

Common side effects of L-tyrosine (≥ 1 in 100): Nausea and abdominal pain, Headache, Insomnia when taken in the afternoon or evening, Palpitations. See the Safety section for uncommon and serious reactions.

Is L-tyrosine safe during pregnancy?

Safe in food-derived amounts. Safety of pharmacological doses above 1 g/day in pregnancy has not been studied. In PKU the metabolic centre sets the dose and composition of replacement therapy.

Is L-tyrosine compatible with breastfeeding?

Compatible. Tyrosine is naturally present in human milk and dietary protein. Supplemental doses do not cause clinically significant infant exposure.

Who should not take L-tyrosine?

L-tyrosine is contraindicated in: Hypersensitivity to tyrosine; Hyperthyroidism and thyrotoxicosis; Non-selective MAO inhibitors; Melanoma (theoretical risk of tyrosinase stimulation); Phaeochromocytoma. Full list in the Safety section.

Other drugs in this group

Licorice root (Glycyrrhiza glabra, root and rhizome; including deglycyrrhizinated DGL), Lion's Mane Mushroom (Hericium erinaceus), Medium-chain triglycerides (MCT, coconut oil C8–C10), N-acetyl-L-tyrosine, Taurine, Beta-alanine, Gamma-aminobutyric acid (GABA), L-citrulline (free form and L-citrulline malate for sports formulas)