A reference work, not a recommendation to use: this profile describes mechanism and evidence and does not replace medical advice. The claims come from marketing and forums and are tested here, not endorsed.

Mechanism of action

Evidence map: L-Tyrosine

Each line stands for a published finding; line style and color show where it comes from. The filter hides weaker evidence levels. Sources: see references.

Tyrosine is the substrate of tyrosine hydroxylase, which catalyzes the rate-limiting step in the synthesis of dopamine, noradrenaline and adrenaline. Unlike for most neurotransmitters, the rate of synthesis here depends on the local substrate concentration; more tyrosine in the brain increases catecholamine synthesis, but only in actively firing neurons [1]. For a long time, tyrosine hydroxylase was regarded as nearly saturated under normal conditions. However, microdialysis experiments in rats showed that more tyrosine in the striatum and in the prefrontal cortex markedly increases DOPA formation [2].

From the behavioral studies, a review concludes that tyrosine improves cognition mainly when dopamine or noradrenaline is temporarily depleted by acute stress or high demands, while the transmitter system itself is intact [3]. For the treatment of diseases or for physical performance, the same review sees little potential [3].

Targets

TargetTypeActionKey dataEvidence
Tyrosine hydroxylaseEnzymeBindingSubstrate of the rate-limiting step; DOPA formation increased with more tyrosine (rat) Animal study[1][2]

Effect profile

Which signaling systems the compound affects according to current data. ↑ enhanced, ↓ dampened, ≈ modulated, ○ no effect; dots = evidence level.

  • Dopamine↑ · More DOPA formation in the striatum and prefrontal cortex with a higher tyrosine supply (rat)[1][2]
  • Noradrenaline↑ · Catecholamine synthesis rises with the tyrosine supply, mainly in active neurons (review, animal data)[1]
  • Serotoninno data
  • Acetylcholineno data
  • Glutamate · AMPAno data
  • Glutamate · NMDAno data
  • GABAno data
  • Histamineno data
  • Orexinno data
  • Adenosineno data
  • Opioidsno data
  • Melatoninno data
  • Neurotrophinsno data
  • Blood flowno data
  • Nitric oxideno data
  • Energy metabolismno data
  • Insulin · glucoseno data
  • Inflammation · oxidativeno data
  • Stress axisno data
  • Testosterone axisno data
  • Endocannabinoidsno data
  • Autophagy · senescenceno data
  • Immune systemno data
  • Lipid metabolismno data
  • Coagulation · fibrinolysisno data
  • Methylationno data

Human studies

  • Working memory in the cold

    double-blind, placebo-controlled, repeated measures · healthy · n = 19 · three test days with cold-water exposure

    Measured: Working memory, reaction time, mood, cortisol

    Result: Cold impaired working memory; with tyrosine, more correct answers and shorter processing times.[4]

    Human, randomised

  • Night work with sleep deprivation

    double-blind, placebo-controlled, parallel groups · healthy · one night without sleep

    Measured: Psychomotor performance, vigilance

    Result: Smaller decline in performance in a psychomotor task and fewer lapses, for about 3 hours.[5]

    Human, randomised

  • Cognitive flexibility

    RCT, double-blind, placebo-controlled · healthy · n = 22 · single dose

    Measured: Task-switching costs

    Result: Lower switching costs than with placebo.[6]

    Human, randomised

  • Dependence on the DRD2 genotype

    RCT, double-blind, placebo-controlled · healthy · single dose

    Measured: Stop-signal task, N-back

    Result: Carriers of the T/T genotype benefited more than C/C carriers.[7]

    Human, randomised

  • Older adults, different amounts

    RCT, double-blind, crossover · healthy (17 older adults, 17 younger adults) · n = 34 · single doses

    Measured: Plasma tyrosine, working memory (N-back)

    Result: In older adults, plasma levels rose more, and higher amounts impaired working memory.[8]

    Human, randomised

Risks and warnings

  • Poorer performance in older adults

    In 60- to 75-year-olds, higher amounts impaired working memory, especially with a steep rise in plasma levels [8].

    Human, randomised

  • Little long-term data

    The studies almost exclusively test single doses; one sleep-deprivation study described tyrosine as relatively well tolerated [5]. No long-term studies on isolated tyrosine were found.

    Human, randomised

Fact check: common claims

  • not supported

    “L-Tyrosine boosts focus and motivation in everyday life”

    Benefits show up mainly under acute stress or high demands [3][4][5]; studies of everyday life without such stress are lacking.

  • partly supported

    “L-Tyrosine helps with stress and sleep deprivation”

    Small placebo-controlled studies show smaller performance losses in the cold and during sleep deprivation [4][5]; larger studies are lacking.

  • refuted

    “More L-tyrosine works better”

    In older adults, higher amounts impaired working memory [8].

  • refuted

    “L-Tyrosine works the same in everyone”

    The effect depended on the DRD2 genotype [7] and differed between older and younger adults [8].

Pharmacokinetics

Absorption
Plasma levels rise dose-dependently after intake, more in older than in younger adults [8].
Half-life
Not reported in the studies reviewed.
Metabolism
Converted, among other routes, by tyrosine hydroxylase to DOPA [1][2].
Entry into the brain
High-protein meals raise the tyrosine concentration in the brain [1].

Legal status

Germany
Component of the normal diet (protein); status as an isolated supplement not verified.
EU
Not verified.
USA
Not verified.

Related compounds

N-Acetyl-L-Tyrosinderivative (German only)

Open questions

  • Is there an optimal amount of tyrosine, depending on age and genotype?
  • Does tyrosine help healthy people without acute stress at all?
  • How safe is regular intake over months?

References

  1. Fernstrom JD, Fernstrom MH. Tyrosine, phenylalanine, and catecholamine synthesis and function in the brain. J Nutr. 2007;137(6 Suppl 1):1539S–47S. doi:10.1093/jn/137.6.1539S · PubMed
  2. Brodnik Z, Bongiovanni R, Double M, Jaskiw GE. Increased tyrosine availability increases brain regional DOPA levels in vivo. Neurochem Int. 2012;61(7):1001–6. doi:10.1016/j.neuint.2012.07.012 · PubMed
  3. Jongkees BJ, Hommel B, Kühn S, Colzato LS. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands – a review. J Psychiatr Res. 2015;70:50–7. doi:10.1016/j.jpsychires.2015.08.014 · PubMed
  4. Mahoney CR, Castellani J, Kramer FM, Young A, Lieberman HR. Tyrosine supplementation mitigates working memory decrements during cold exposure. Physiol Behav. 2007;92(4):575–82. doi:10.1016/j.physbeh.2007.05.003 · PubMed
  5. Neri DF, Wiegmann D, Stanny RR, Shappell SA, McCardie A, McKay DL. The effects of tyrosine on cognitive performance during extended wakefulness. Aviat Space Environ Med. 1995;66(4):313–9. PubMed
  6. Steenbergen L, Sellaro R, Hommel B, Colzato LS. Tyrosine promotes cognitive flexibility: evidence from proactive vs. reactive control during task switching performance. Neuropsychologia. 2015;69:50–5. doi:10.1016/j.neuropsychologia.2015.01.022 · PubMed
  7. Colzato LS, Steenbergen L, Sellaro R, Stock AK, Arning L, Beste C. Effects of l-tyrosine on working memory and inhibitory control are determined by DRD2 genotypes: a randomized controlled trial. Cortex. 2016;82:217–24. doi:10.1016/j.cortex.2016.06.010 · PubMed
  8. van de Rest O, Bloemendaal M, de Heus R, Aarts E. Dose-dependent effects of oral tyrosine administration on plasma tyrosine levels and cognition in aging. Nutrients. 2017;9(12):1279. doi:10.3390/nu9121279 · PubMed
How this profile was checked

Last reviewed: 2026-10-23. All sources with a DOI or PMID were resolved automatically via Crossref or doi.org and PubMed.

Translated from the German profile (version of 2026-10-23); translation checked on 2026-10-26.

Checked

  • All DOIs resolved via Crossref and all PMIDs via PubMed with tools/pruefe_profile.py; [5] has no DOI.
  • Abstracts (for [2], species via MeSH: Sprague-Dawley rats): substrate dependence of catecholamine synthesis, only in active neurons, protein raises brain tyrosine [1]; DOPA up to 250% (striatum) and 300% (mPFC), TH probably not saturated [2]; benefit mainly with temporary depletion of catecholamines [3]; n = 19, cold, double-blind [4]; sleep deprivation, double-blind, effect ≈ 3 h, “relatively benign” [5]; n = 22, switching costs ↓ [6]; DRD2 genotype [7]; 17 + 17, impairment with higher amounts [8].
  • ClinicalTrials.gov: 71 entries for “tyrosine supplementation” (October 23, 2026).

Not verified

  • Legal status of L-tyrosine as a dietary supplement in Germany, the EU and the US not checked.
  • The participant numbers of [5] and [7] are not given in the abstract.
  • The frequently mentioned concerns about MAO inhibitors or thyroid disease could not be supported with studies within the scope of this profile and were therefore not included.

No dosages, no sources of supply. This information does not replace medical advice.

Spotted an error or missing something?

Request a compound, suggest an improvement or report an error. Every message is read.

Type of message

The website stores nothing. The button opens your email app with a pre-filled message.