L-Tyrosine

Conditionally essential amino acid, precursor of catecholamines and thyroid hormones

ATC code: A16AA-L-TYROSINE (L-Tyrosine)

Brand names – supplements

Jarrow Formulas L-Tyrosine, NOW Foods L-Tyrosine, Solgar L-Tyrosine, Doctor's Best L-Tyrosine

Supplements are not tested in clinical trials and are not registered as medications.

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.

Indications

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. ESPGHAN and SSIEM 2017 European guidelines include tyrosine in replacement therapy. Self-administered L-tyrosine in PKU does not substitute the prescribed dietary formulas; the metabolic centre team sets the regimen and doses.

Sources

ESPGHAN/SSIEM: Key European guidelines for the diagnosis and management of patients with phenylketonuria (2017)

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.

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

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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

PregnancyFDA C

FDA Category C. 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

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.

Frequently asked

What is L-Tyrosine used for?

L-Tyrosine is evaluated for the following indications with varying evidence strength: Phenylketonuria (evidence tier A), Cognitive performance under acute stress (evidence tier C). 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?

FDA category C. FDA Category C. 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.

Mechanism of action

Indications

Phenylketonuria

Adjunct

Sources

ESPGHAN/SSIEM: Key European guidelines for the diagnosis and management of patients with phenylketonuria (2017)

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

PregnancyFDA C

Breastfeeding

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.

Frequently asked

What is L-Tyrosine used for?

What are the side effects of L-Tyrosine?

Is L-Tyrosine safe during pregnancy?

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?