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Moderate evidenceBrain & cognition

L-Tyrosine

Tyrosine reliably protects cognitive performance when the brain is depleted by acute stress such as cold, noise, or sleep loss, but it does essentially nothing for cognition in rested, unstressed people.

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What the science says

  • Preserves working memory and cognitive flexibility under acute stress Moderate evidence

    A review of the human literature found tyrosine consistently reduced cognitive decline under short-term physically or psychologically demanding conditions, including cold exposure, loud noise, hypoxia and one night of sleep deprivation, at doses of 100-150 mg/kg (roughly 7-12 g) given 30-60 minutes beforehand. The mechanism is replenishing catecholamine precursors depleted by acute stress.

  • No meaningful benefit in rested, unstressed people Limited evidence

    The same review found that when catecholamines are not depleted, tyrosine produces no reliable improvement in memory, attention or reaction time, and may even impair performance in people whose dopamine function is already optimal. It is a stress buffer, not a general cognitive enhancer.

  • Does not improve outcomes in phenylketonuria Limited evidence

    A Cochrane review of 4 randomized crossover trials in phenylketonuria found that although tyrosine supplementation raised blood tyrosine concentrations, there was no evidence of benefit on any measured neuropsychological or clinical outcome. This is a clean negative result in the population where the biochemical rationale is strongest.

  • No credible evidence for physical performance or fat loss Limited evidence

    Trials of tyrosine as an ergogenic aid, including exercise in the heat, have generally shown no improvement in endurance or power output. Its presence in fat-burner formulas is based on thyroid-hormone-precursor reasoning that has not translated into human weight-loss data.

Dosage & safety

Studied doseAcute stress protocols used 100-150 mg/kg body weight (roughly 7-12 g) taken 30-60 minutes before the stressor. Commercial supplements commonly supply 500-2000 mg, which is well below the dose used in most positive trials.
SafetyGenerally well tolerated; gram doses can cause nausea, headache, heartburn and fatigue. Contraindicated with MAO inhibitors (risk of hypertensive crisis) and should be used cautiously with levodopa, which competes for the same amino acid transporter. People with hyperthyroidism or Graves' disease are usually advised to avoid it since tyrosine is a thyroid hormone precursor. Avoid in melanoma without medical advice, given tyrosine's role in melanin synthesis.

How to take it

Timing30-60 minutes before the stressful or sleep-deprived period you are trying to cover; it does nothing useful taken at random.
With food?On an empty stomach — a protein-rich meal supplies competing amino acids that blunt the effect.
Worth knowingThe trials used 7-12 g; a 500 mg capsule is not a smaller version of that dose, it is a different thing entirely.

Interactions

With medications

  • MAO inhibitors (phenelzine, tranylcypromine, selegiline)

    Tyrosine is a catecholamine precursor, and the combination risks a hypertensive crisis. do not combine

  • levodopa

    Tyrosine and levodopa compete for the same amino acid transporter, so tyrosine can reduce how much levodopa gets absorbed and into the brain. separate by at least 2 hours and tell your neurologist

  • thyroid hormone and antithyroid drugs

    Tyrosine is a thyroid hormone precursor, which is why it is generally avoided in hyperthyroidism and Graves' disease. avoid if you have an overactive thyroid; discuss with your prescriber otherwise

With other supplements

  • 5-HTP and L-tryptophan

    They compete for the same blood-brain barrier transporter, so each reduces the other's brain uptake. separate by at least 2 hours

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does L-tyrosine improve focus?

Only under acute stress — the evidence is moderate. L-tyrosine preserves working memory during cold, noise or sleep loss, but in rested, unstressed people it gives no reliable cognitive benefit.

How much L-tyrosine should I take?

The positive trials used 100–150 mg/kg, roughly 7–12 g, taken 30–60 minutes before the stressor on an empty stomach. The 500–2000 mg in typical L-tyrosine supplements is well below that.

Does tyrosine help with weight loss or workouts?

No — the evidence is limited. Trials of L-tyrosine for endurance or power have generally been null, and there are no human weight-loss data behind its use in fat burners.

Is L-tyrosine safe with medications?

Never combine L-tyrosine with MAO inhibitors, because of the risk of a hypertensive crisis. It competes with levodopa, so separate them by at least 2 hours, and avoid it with an overactive thyroid.

Scientific references

Where to buy

NOW Foods, L-Tyrosine Pure Powder, 4 oz (113 g)

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