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Tyrosine

Supplement amino acid brain & moodenergy
Aka: L-tyrosine, N-acetyl-L-tyrosine, NALT
Brands seen in Singapore: California Gold Nutrition, NOW Foods, Doctor's Best, Natural Factors, Jarrow Formulas
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
Short-term stress or heavy mental load · effects vary
When to take
Daily
Studied for
The 4 g/day safety trial ran 4 weeks
Pros & cons
Pros
  • Cognition better under short-term stress or load
  • Up to 4 g/day for 4 weeks was tolerated in 30 men
  • SG listings run 500–750 mg a capsule
Cons
  • Reports on effectiveness vary considerably
  • Physical-exercise potential looks minimal
  • Safety data is 4 weeks, 30 healthy men, one trial
Sources
  1. Effect of tyrosine supplementation on clinical and healthy populations under stress or cognitive demands — a review (Jongkees et al., J Psychiatr Res 2015;70:50-57; PMID 26424423) — conclusion · read 2026-08-27
    what it says
    “TYR does seem to effectively enhance cognitive performance, particularly in short-term stressful and/or cognitively demanding situations. We conclude that TYR is an effective enhancer of cognition, but only when neurotransmitter function is intact and DA and/or NE is temporarily depleted.”
  2. Jongkees et al., J Psychiatr Res 2015 — variability across studies · read 2026-08-27
    what it says
    “reports on the effectiveness of TYR supplementation vary considerably, with some studies finding beneficial effects, whereas others do not”
  3. Jongkees et al., J Psychiatr Res 2015 — limits in clinical disorders and physical exercise · read 2026-08-27
    what it says
    “The potential of using TYR supplementation to treat clinical disorders seems limited … Likewise, the potential of TYR supplementation for enhancing physical exercise seems minimal as well”
  4. Evaluation of the Safety and Tolerability of L-Tyrosine Supplementation in Healthy Adult Men: A Randomized Crossover Trial (Nutrients 2026; PMID 42356406) — conclusion · read 2026-08-27
    what it says
    “Four-week supplementation with L-tyrosine at doses up to 4 g/day was well tolerated in healthy adult men and was not associated with biochemical and clinically relevant adverse effects under the conditions of this study.”
  5. L-Tyrosine safety and tolerability crossover trial (Nutrients 2026) — design and doses · read 2026-08-27
    what it says
    “In a randomized, double-blind, placebo-controlled crossover trial, 30 healthy adult men received L-tyrosine at graded daily doses (0, 1, 2, 3, or 4 g/day)”
  6. L-Tyrosine safety and tolerability crossover trial (Nutrients 2026) — NOAEL statement · read 2026-08-27
    what it says
    “These findings suggest that 4 g/day represents the highest tested intake level without observable adverse effects and may serve as the NOAEL”
  7. HSA — Health Supplements Guidelines GL-CHPB-3-001 Rev. 020 (January 2026), s3.1 working definition + clause 4.8 · read 2026-08-27
    what it says
    “Vitamins, minerals, amino acids, fatty acids, enzymes, probiotics and other bioactive substances … HS for use by the general adult population should not contain vitamins and minerals exceeding the stipulated limits stated in Tables 4 and 5.”
  8. HSA — Guidelines on Prohibited and Restricted Ingredients in HS and TM, GL-CHPB-1-012 Rev. 001 (Oct 2025), clause 1.3 + Annex A/B — searched, no row for tyrosine · read 2026-08-27
    what it says
    “The objective of this guideline is to highlight the substances of concern when used in HS and TM and is not meant to be an exhaustive list.”
  9. iHerb Singapore — 'L-Tyrosine' category page, default order, 1 - 43 of 43 results · read 2026-08-27
    what it says
    “California Gold Nutrition, Adrenal Support with L-Tyrosine … NOW Foods, L-Tyrosine, 500 mg … NOW Foods, L-Tyrosine, 750 mg … Doctor's Best, L-Tyrosine, 500 mg … Natural Factors, L-Tyrosine, 500 mg … Jarrow Formulas, L-Tyrosine, 500 mg”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.