NutriDex

The Supplement Research Compendium
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L-Tyrosine

Amino acid that may protect thinking under acute stress.

Preliminary evidence 🧠Nootropic⚡Performance

✚ Updated · How we grade evidence

Evidence tier
Preliminary
Research weight
Citations
9 verified / 9
Classification
Nootropic
❝
What the evidence says. Graded preliminary: tyrosine is a catecholamine precursor and small acute-dose RCTs show benefits when the brain is depleted by cold, sleep loss or heavy cognitive demand, but trials are tiny, single-dose and crossover, effects fade within hours, several tasks show null or mixed results, and there is no evidence it helps cognition at rest or with daily use. (Preliminary evidence: Early or small human trials; promising but not yet conclusive.)

What is L-Tyrosine?

L-Tyrosine is a nootropic used for cognition under acute stress. NutriDex grades the human evidence as Preliminary. L-Tyrosine is an amino acid the body uses to make the catecholamines dopamine and noradrenaline. The interest is in 'topping up' these neurotransmitters when stress depletes them. In small double-blind RCTs, a single large dose (100–150 mg/kg) blunted the cognitive and mood decline caused by cold, hypoxia, prolonged wakefulness or demanding multitasking, and improved working memory, task-switching and inhibitory control versus placebo. Effects are modest and short-lived (often ~3 hours). A 2015 systematic review of 10 RCTs gave only a weak, qualified recommendation, judging the overall evidence insufficient. Results are also state-dependent: benefits appear mainly in depleted or genetically dopamine-low individuals, and some tasks show no effect or even worse performance, including reduced working memory at high doses in older adults. There is no good evidence it boosts cognition in unstressed people or with chronic daily use.

Purported Benefits

✓Cognition under acute stress
✓Working memory & flexibility
✓Resist cold / sleep-loss decline
✓Focus while multitasking

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Cognition under acute stress (cold/hypoxia/sleep loss)Small RCTs show single large doses blunt stress-induced decline; effect short-lived (~3 h) and state-dependent. Preliminary ↑ benefit · small 2
Working memory & cognitive flexibilitySome RCTs show gains, but effects depend on genotype and high doses worsened working memory in older adults. Mixed ↔ mixed · small 3
Overall cognitive-enhancement claimSystematic review of 10 RCTs gave only a weak, qualified recommendation; evidence judged insufficient. No Evidence ↔ mixed 1
Endurance exercise performanceGRADE meta-analysis found no effect on time-to-exhaustion or time-trial performance vs placebo. Moderate — no effect · negligible 1

Dosing & Compounds

Typical Dose
Single acute doses of 100–150 mg/kg (≈7–12 g) taken ~30–60 min before a stressor; ~2 g/day is the common over-the-counter amount.
Active Compounds
L-Tyrosine (free amino acid)

Safety & Cautions

Tyrosine is generally well tolerated at typical doses; large acute doses can cause nausea, headache, heartburn or fatigue, and a dose-response trial found higher doses worsened working memory in older adults. Because it feeds catecholamine and thyroid-hormone synthesis, avoid or use caution with MAOI antidepressants (risk of hypertensive reaction), levodopa (competes for absorption, may blunt Parkinson's treatment), thyroid medication or hyperthyroidism (Graves' disease), and stimulants. People with phenylketonuria should follow medical advice. Discuss with a clinician before use if pregnant, breastfeeding, or on these medications. Educational only — always check with your doctor or pharmacist before combining L-Tyrosine with any medicine.

L-Tyrosine drug interactions

Known or theoretical interactions between L-Tyrosine and common medications — educational, not exhaustive. Always check with your doctor or pharmacist before combining L-Tyrosine with any medicine.

Caution
MAOIs (phenelzine, tranylcypromine)
Theoretical risk of raised blood pressure; monitor when combined with MAOI antidepressants.
Tyrosine is a catecholamine precursor; with MAO inhibited, increased catecholamine synthesis could elevate blood pressure. NIH PMC — Supplemental L-tyrosine with phenelzine: clinical review · NIH StatPearls — MAOIs
Monitor
Thyroid medications (levothyroxine, antithyroid)
May theoretically affect thyroid hormone levels; monitor thyroid function if combined with thyroid drugs.
Tyrosine is a building block of thyroid hormones (T3/T4), so supplementation could influence thyroid hormone status. NIH StatPearls — Biochemistry, Tyrosine

Key Studies

Systematic review and meta-analysis Solon-Junior et al. 2024 ✓ PubMed
A systematic review and GRADE meta-analysis of human trials found tyrosine supplementation was ineffective for endurance performance, with no difference from placebo for time-to-exhaustion (SMD = 0.02, p = 0.94) or time-trial performance (SMD = -0.04, p = 0.85) at moderate-quality evidence.
Systematic review Attipoe 2015 ✓ PubMed
Systematic review of 10 RCTs + 4 trials: only a weak recommendation for cognitive stress; evidence judged insufficient for firm conclusions.
RCT McAllister et al. 2024 ✓ PubMed
In an 80-person double-blind RCT, a single 2,000 mg dose of L-tyrosine before a virtual-reality active-shooter stress drill produced significantly fewer missed responses on the Stroop task versus placebo, though it did not change stress biomarkers (salivary alpha-amylase, sIgA) or heart rate.
RCT Steenbergen 2015 ✓ PubMed
2 g tyrosine reduced task-switching costs, promoting cognitive flexibility vs placebo in 22 healthy adults (double-blind crossover).
RCT Colzato 2016 ✓ PubMed
Working-memory and inhibitory-control benefits depended on DRD2 genotype: T/T carriers gained more than C/C, so response varies by dopamine genetics.
RCT Stock 2018 ✓ PubMed
Mixed/null result: tyrosine shrank consciously perceived conflict in a Simon task but not a Flanker task, and worsened subliminal conflict (n=26).
RCT van de Rest 2017 ✓ Full text
Dose-response trial: higher tyrosine doses gave WORSE working memory in older adults (60–75 y), suggesting overshoot can impair, not help.
RCT Neri 1995 ✓ PubMed
150 mg/kg during a night of sleep loss reduced psychomotor decline and vigilance lapses; benefit lasted ~3 hours (double-blind RCT).
RCT Thomas 1999 ✓ PubMed
Tyrosine improved accuracy and reduced errors on working-memory tasks during a demanding multitasking battery vs placebo.
9 sources cited · 9 verified Search all studies on PubMed ↗

Common questions about L-Tyrosine

What is L-Tyrosine used for?

L-Tyrosine is most often taken for Cognition under acute stress, Working memory & flexibility, Resist cold / sleep-loss decline, Focus while multitasking. Amino acid that may protect thinking under acute stress.

Does L-Tyrosine work — what does the evidence say?

Preliminary evidence. Early or small human trials; promising but not yet conclusive. L-Tyrosine is an amino acid the body uses to make the catecholamines dopamine and noradrenaline. The interest is in 'topping up' these neurotransmitters when stress depletes them. In small double-blind RCTs, a single large dose (100–150 mg/kg) blunted the cognitive and mood decline caused by cold, hypoxia, prolonged wakefulness or demanding multitasking, and improved working memory, task-switching and inhibitory control versus placebo. Effects are modest and short-lived (often ~3 hours). A 2015 systematic review of 10 RCTs gave only a weak, qualified recommendation, judging the overall evidence insufficient. Results are also state-dependent: benefits appear mainly in depleted or genetically dopamine-low individuals, and some tasks show no effect or even worse performance, including reduced working memory at high doses in older adults. There is no good evidence it boosts cognition in unstressed people or with chronic daily use.

What is the typical dose of L-Tyrosine?

Single acute doses of 100–150 mg/kg (≈7–12 g) taken ~30–60 min before a stressor; ~2 g/day is the common over-the-counter amount.

Is L-Tyrosine safe? Any cautions or side effects?

Tyrosine is generally well tolerated at typical doses; large acute doses can cause nausea, headache, heartburn or fatigue, and a dose-response trial found higher doses worsened working memory in older adults. Because it feeds catecholamine and thyroid-hormone synthesis, avoid or use caution with MAOI antidepressants (risk of hypertensive reaction), levodopa (competes for absorption, may blunt Parkinson's treatment), thyroid medication or hyperthyroidism (Graves' disease), and stimulants. People with phenylketonuria should follow medical advice. Discuss with a clinician before use if pregnant, breastfeeding, or on these medications.

How many studies support L-Tyrosine?

NutriDex cites 9 sources for L-Tyrosine, graded "Preliminary".

Does L-Tyrosine interact with any medications?

Yes — known or theoretical interactions include: MAOI antidepressants (caution), Thyroid medications (levothyroxine, antithyroid) (monitor). This is educational and not exhaustive; always check with your doctor or pharmacist before combining L-Tyrosine with any medicine.

Cite this page
APA

Peh, D. (2026). L-Tyrosine: Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/l-tyrosine

BibTeX
@misc{nutridex_l_tyrosine,
  author       = {Peh, Daryl},
  title        = {L-Tyrosine: Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/l-tyrosine},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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