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Phenylalanine

Supplement amino acid general nutrition
Aka: DL-phenylalanine, DLPA, L-phenylalanine
Brands seen in Singapore: Life Extension, NOW Foods, Swanson, Vitacost, Source Naturals
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
The body converts it to tyrosine · few human trials
Pros & cons
Pros
  • The body's route from phenylalanine to tyrosine
  • Not listed in HSA's prohibited or restricted annexes
Cons
  • Phenylketonuria — a lifelong phe-restricted diet
  • No human supplement RCT surfaced in a 274-hit search
  • The human literature is about pku, not supplements
Sources
  1. Positron Emission Tomography (PET) in Phenylketonuria: A Systematic Review of Brain Metabolism Beyond Phenylalanine (Am J Med Genet A 2026; PMID 42361219) · read 2026-08-27
    what it says
    “PKU impairs the conversion of Phe to tyrosine and causes excess phenylalanine to accumulate. This accumulation can competitively block some other amino acids from entering the brain.”
  2. PET in Phenylketonuria systematic review (Am J Med Genet A 2026) — neurotransmitters · read 2026-08-27
    what it says
    “This may reduce production of key neurotransmitters like dopamine and serotonin, which can affect brain function and development.”
  3. A food pyramid for adult patients with phenylketonuria and a systematic review on the optimal dietary treatment of adult patients with PKU (Rondanelli et al., Clin Nutr 2023; PMID 37001196) · read 2026-08-27
    what it says
    “Early dietary treatment is mind-saving in patients with phenylketonuria. A "diet-for-life" is advocated, aimed to prevent effects of chronic exposure to hyperphenylalaninemia.”
  4. Europe PMC REST search, 27 Aug 26 — phenylalanine in title plus supplementation/requirement/safety/phenylketonuria (774 hits, PKU-dominated; no human supplementation trial in the first page of results) · read 2026-08-27
    what it says
    “"hitCount":774 … "Is Phenylalanine Restricted Dietary Treatment in Phenylketonuria Associated with Disordered Eating: A Systematic Review."”
  5. Europe PMC REST search, 27 Aug 26 — DL-phenylalanine / D-phenylalanine / phenylalanine supplementation in title (274 hits; the results are synthesis chemistry, biosensors, nanomaterials and rodent work, not human supplementation trials) · read 2026-08-27
    what it says
    “"hitCount":274 … "Site-specifically immobilized D-amino acid dehydrogenase for the synthesis of D-phenylalanine" … "Neuroprotective Potential of Chromium-D-Phenylalanine … Rotenone-Induced Parkinsonism in Rats"”
  6. HSA Health Supplements Guidelines GL-CHPB-3-001 Rev. No. 020 (January 2026) — s3.1 working definition and clause 4.8 (Tables 4-5 cover vitamins and minerals only) · 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.”
  7. HSA Guidelines on Prohibited and Restricted Ingredients in HS and TM, GL-CHPB-1-012 Rev. No. 001 (Oct 2025), Annex A/B — full text searched 27 Aug 26, no row for phenylalanine · 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.”
  8. iHerb Singapore category page "L-Phenylalanine Supplements", default best-selling order, first 5 distinct brands · read 2026-08-27
    what it says
    “L-Phenylalanine Supplements”
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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.