Supplement analysis backed by scientific evidence · PT

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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.

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.

Scientific references

Where to buy

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

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