Amino Acid

N-Acetyl L-Tyrosine

(2S)-2-acetamido-3-(4-hydroxyphenyl)propanoic acid

Evidence TierDWADA NOT PROHIBITED

tuneTypical Dose

not established for nootropic outcomes

watchEffect Window

Metabolic effect in PN is dose/formulation dependent. Performance claims are acute and context-specific if any.

check_circleCompliance

WADA NOT PROHIBITED

Overview

Clinical Summary

N-acetyl L-tyrosine is a more soluble tyrosine derivative used for catecholamine precursor support. Direct oral evidence is weak, and plain L-tyrosine has the stronger human record.

Intended effects mirror tyrosine, supporting cognitive performance under acute stressors such as sleep deprivation or cold exposure, but direct trials of N-acetyl tyrosine are limited. Some users report improved alertness, especially with caffeine. Minority claims include mood improvement, but controlled evidence is weak. Net benefit is most plausible when formulation solubility matters more than maximal tyrosine delivery.

Acetylated precursor/tyrosine-source formulation in clinical nutrition. Cognitive/performance claims for NALT are indirect via tyrosine literature.

Outcomes

What This Is Expected To Influence

Primary Outcomes

  • Primary evidence supports amino-acid retention in adult parenteral nutrition. Direct nootropic outcome evidence is sparse.

Secondary Outcomes

  • Ancillary tyrosine data suggest possible acute cognitive-flexibility benefit under stress. Sleep-deprivation study showed no benefit.

Safety

Contraindications and Interactions

Contraindications

  • Pregnancy
  • Lactation
  • Uncontrolled thyroid/cardiovascular disease
  • Severe psychiatric instability
  • Severe renal/hepatic impairment

Side effects

  • Headache
  • Nausea
  • Heartburn

Interactions

  • Dopaminergic drugs
  • MAO inhibitors
  • Stimulants
  • Thyroid replacement

Avoid if

  • Active mania
  • Severe anxiety disorder
  • Hypertension
  • Uncontrolled endocrine disease

Evidence

Study-level References

n-acetyl-l-tyrosine-SRC-001Clinical study
Sourceopen_in_new

Hoffer LJ, Sher K, Saboohi F, Bernier P, MacNamara EM, Rinzler D. N-acetyl-L-tyrosine as a tyrosine source in adult parenteral nutrition. JPEN Journal of Parenteral and Enteral Nutrition. 2003;27(6). doi:10.1177/0148607103027006419. PMID:14621123.

Population: Adults receiving continuous parenteral nutrition

Dose protocol: NALT-containing Aminosyn II 15% PN infusion in adults with normal metabolism

Key findings: Approximately 35% of administered NALT was excreted unchanged in urine. Retained fraction was sufficient to meet aromatic amino acid requirements.

Notes: Strongest direct NALT evidence in this dataset.

Paper content

Approximately 35% of parenterally administered N-acetyl-L-tyrosine was excreted unchanged in the urine, with no important effect of infusion rate, nitrogen balance, or renal function on this value. Despite the substantial urinary losses, sufficient NAT was retained at standard dosing to meet the combined aromatic amino acid needs of adults with normal phenylalanine hydroxylase activity.

n-acetyl-l-tyrosine-SRC-002Animal study
Sourceopen_in_new

Im HA, Meyer PD, Stegink LD. N-acetyl-L-tyrosine as a tyrosine source during total parenteral nutrition in adult rats. Pediatr Res. 1985;19(6). doi:10.1203/00006450-198506000-00002. PMID:3925425.

Population: Adult male rats receiving total parenteral nutrition

Dose protocol: Radiolabeled NALT infused as part of TPN regimen in adult rats at two dose levels

Key findings: Dose-dependent utilization confirmed. Urinary losses rose with higher infusion levels, with tissue labeling and protein incorporation tracked.

Notes: Rat model. Species and route mismatch vs oral human use.

Paper content

N-acetyl-L-tyrosine was studied as a soluble tyrosine source for parenteral nutrition in rats. At both infusion levels, the compound was rapidly utilized with labeling of tissue tyrosine pools, CO2 production, and protein incorporation, though urinary losses increased at higher doses.

n-acetyl-l-tyrosine-SRC-003RCT
Sourceopen_in_new

Steenbergen L, Sellaro R, Hommel B, Colzato LS. Tyrosine promotes cognitive flexibility: evidence from proactive vs. reactive control during task switching performance. Neuropsychologia. 2015;69:50-55. doi:10.1016/j.neuropsychologia.2015.01.022. PMID:25598314.

Population: Healthy young adult females

Dose protocol: Single oral dose of L-tyrosine vs placebo in 22 healthy adults (double-blind RCT)

Key findings: Tyrosine reduced task-switching costs compared to placebo, supporting improved cognitive flexibility.

Notes: Small sample. Used L-tyrosine, not NALT, so translation is indirect.

Paper content

This double-blind, randomized, crossover study investigated whether tyrosine supplementation promotes cognitive flexibility during task switching. Tyrosine, a dietary amino acid that increases brain dopamine levels, enhanced proactive control during task switching performance. The findings support the role of dopamine in cognitive flexibility and suggest tyrosine can improve cognitive control under demanding conditions.

n-acetyl-l-tyrosine-SRC-004RCT
Sourceopen_in_new

Waters WF, Magill RA, Bray GA, Volaufova J, Smith SR, Lieberman HR, Rood J, Hurry M, Anderson T, Ryan DH. A comparison of tyrosine against placebo, phentermine, caffeine, and D-amphetamine during sleep deprivation. Nutritional Neuroscience. 2003;6(4). doi:10.1080/1028415031000120543. PMID:12887139.

Population: Healthy males subjected to 40.5 hours of sleep deprivation

Dose protocol: Tyrosine 150 mg/kg vs placebo, phentermine, caffeine, and D-amphetamine over 40.5 h sleep deprivation in 76 healthy males

Key findings: Tyrosine had no significant effect on sleep-related performance measures compared to placebo, but did stimulate prolactin release.

Notes: Male-only, protocol-specific outcomes. Used L-tyrosine, not NALT.

Paper content

In 76 healthy males after 36 hours without sleep, tyrosine (150 mg/kg) had no significant effect on any sleep-related measure compared to placebo, though it stimulated prolactin release. D-amphetamine markedly decreased sleep drive but impaired many aspects of recovery sleep. Phentermine and caffeine both reduced sleep drive, but phentermine impaired REM recovery sleep.

n-acetyl-l-tyrosine-SRC-005Animal study
Sourceopen_in_new

Yeghiayan SK, Luo S, Shukitt-Hale B, Lieberman HR. Tyrosine improves behavioral and neurochemical deficits caused by cold exposure. Physiology & Behavior. 2001;72(3). doi:10.1016/s0031-9384(00)00398-x. PMID:11274672.

Population: Male Fischer 344 rats subjected to acute cold stress and hypothermia

Dose protocol: Tyrosine administered to rats under acute cold-exposure stress

Key findings: Dose-dependent improvement in behavioral performance and norepinephrine levels under cold stress.

Notes: Animal model with co-intervention design. Limits direct supplementation inference for humans.

Paper content

Tyrosine, amphetamine, and phenylpropanolamine each dose-dependently improved forced swim performance in rats subjected to acute hypothermia. Combining tyrosine with amphetamine or phenylpropanolamine produced additional improvements. Microdialysis revealed that tyrosine further elevated hippocampal norepinephrine concentrations under cold stress, supporting the role of enhanced noradrenergic function in stress resilience.

n-acetyl-l-tyrosine-SRC-006Official policy document
Sourceopen_in_new

World Anti-Doping Agency, The List of Prohibited Substances and Methods, official page, https://www.wada-ama.org/en/content/what-is-prohibited.

Population: 2026 public list materials and searchable classes/updates

Key findings: No named N-acetyl-L-tyrosine entry identified in listed classes/summary materials. Athlete status cannot be inferred from absence alone.

Notes: Negative finding is based on public list documentation and naming/categorization conventions. Verify the current list before competition use.

Paper content

No named N-acetyl-L-tyrosine entry identified in listed classes/summary materials; athlete status cannot be inferred from absence alone.

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