L-tyrosine
NALT / N-acetyl L-tyrosine · Brain
Dopamine precursor studied under acute stress, cold, sleep loss, heavy multitasking.
What it is
An amino acid that is the raw material for dopamine, adrenaline and noradrenaline. Its evidence has an unusual shape: effects are mixed overall, and appear most likely when catecholamines are being depleted, by cold, noise, sleep loss, or genuinely demanding cognitive work.
How it works
Under acute stress or heavy cognitive load, the brain can burn through catecholamines faster than it resupplies them. Supplemental tyrosine gives the synthesis pathway more substrate. The effect appears largest when depletion is happening, though some placebo-controlled studies in rested adults doing demanding working-memory tasks also found benefit, so "only under stress" overstates it.
Which form to buy
The form in essentially all the military and stress-performance research, at gram-level amounts.
The default.
Sold as better absorbed. The substantial-excretion finding comes from INTRAVENOUS use in parenteral nutrition, not oral supplements, and no oral head-to-head comparison exists.
No demonstrated oral advantage over plain L-tyrosine; comparative evidence is sparse.
Usually far below the amounts used in the stress research.
Decorative quantities.
What it actually does, graded
The most consistent finding, across military and lab studies. Note those classic studies often used weight-based amounts far above typical supplement servings.
Some positive results in high-load tasks.
Mixed: placebo-controlled trials found task-specific gains in rested adults on demanding working-memory and task-switching paradigms, while other rested-person studies were null or depended on baseline.
Tested and unsupported despite the dopamine-precursor logic.
Mixed, with some signal specifically in heat stress.
Pros and cons
- A rare supplement with a clearly defined condition where it works
- Cheap and well tolerated
- Non-stimulant in itself
- Effects are inconsistent, and the largest signals come from stressed or heavily loaded conditions
- The trendy NALT form is probably the worse choice
- A labelled contraindication with MAOIs, and open questions around thyroid medication
What to expect
- Studies dosed acutely before testing under the stressor or cognitive load.
- Rested and comfortable: results are genuinely mixed, some tasks improved, many did not.
Interactions
Is it for you?
- Sleep-deprived performance demands, cold exposure, high-stakes cognitive load
- Shift workers and anyone whose hard days are genuinely depleting
- You expect a reliable everyday nootropic effect, the rested-person results are genuinely mixed
Who should avoid it
- Anyone on phenelzine or another MAOI, the drug label contraindicates the combination
- People on thyroid medication or L-DOPA, without prescriber input
Research on this supplement
Papers about this supplement, not proof of the claims above. A title says what was studied, which is sometimes a negative result or a different question entirely.
- O-(2-[18F]-Fluoroethyl)-L-Tyrosine (FET) in Neurooncology: A Review of Experimental Results
- Yeast: A platform for the production of (L) -tyrosine derivatives
- L-Tyrosine Limits Mycobacterial Survival in Tuberculous Granuloma
What the evidence says
Small human trials show benefit specifically under acute stressors. There is little evidence it does anything on a normal, rested day.
What studies used
500-2,000 mg. 30-60 min before the demand.
Reported from published studies and product labelling — a record of what was used in research, not a recommendation. What is right for you is a conversation with a clinician.
Evidence base
established literature
Strong human evidence: either a phase 3 or 4 trial report alongside review-level evidence, or ten or more randomised controlled trial reports.
This letter measures how much human research exists, not whether it works for you — the tier above (Limited) is the read on quality.
Research (12)
- Recent advances in biocatalytic derivatization of L-tyrosineAppl Microbiol Biotechnol · 2020
- O-(2-[18F]-Fluoroethyl)-L-Tyrosine (FET) in Neurooncology: A Review of Experimental ResultsCurr Radiopharm · 2019
- Yeast: A platform for the production of (L) -tyrosine derivativesYeast · 2023
- L-Tyrosine Limits Mycobacterial Survival in Tuberculous GranulomaPathogens · 2023
- Current trends in the use of O-(2-[(18)F]fluoroethyl)-L-tyrosine ([(18)F]FET) in neurooncologyNucl Med Biol · 2021
- l-tyrosine modulates biofilm formation of Bacillus cereus ATCC 14579Res Microbiol · 2023
- Terahertz tyrosine modesSpectrochim Acta A Mol Biomol Spectrosc · 2023
- Towards defining receptors for L-tyrosine and L-dopaMol Cell Endocrinol · 1994
- Enhancing the efficiency of L-tyrosine by repeated batch fermentationBioengineered · 2020
- Production of L-tyrosine using tyrosine phenol-lyase by whole cell biotransformation approachEnzyme Microb Technol · 2019
- N-Acetyl-3,5-dibromo-l-tyrosine hemihydrateActa Crystallogr Sect E Struct Rep Online · 2012
- L-tyrosine in depressionLancet · 1980
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