{"ok":true,"entry":{"slug":"methionine","kind":"supplement","name":"methionine","aliases":["L-methionine"],"brands_sg":["NOW Foods","Swanson","Nutricost","Nutricology","Source Naturals"],"class":"amino acid","tags":["general"],"use_for":"an indispensable amino acid · the body's main methyl donor","use_after":null,"use_duration":null,"take_with":"b6, b12, folate and c moderate its homocysteine effect","pros":["unique among essential amino acids for its sulfur atom","precursor of cysteine and of glutathione","minimum need in adults 60+ measured at 5.1 mg/kg/day"],"cons":["intakes over ~5x normal raised homocysteine levels","a mistaken 10-fold overdose resulted in death","known to worsen symptoms in schizophrenia"],"dose_note":"nutritional and metabolic studies used amounts both below and above the requirement without reported adverse effects in adults and children; a 0.1 g/kg 'loading dose' is a research test of homocysteine response, not a supplement dose","dosage":{"ul":null,"unit":"mg","fda_dv":null,"rda_ai":null,"ul_status":"none_established","population":"general adult","hsa_max_daily":null},"ul_status":"none_established","sg_class":null,"cautions":["schizophrenia — methionine is known to exacerbate psychopathological symptoms in these patients","raised homocysteine or vascular concerns — its role as a homocysteine precursor is the most notable flagged risk","infants — intakes of 2-5 times normal impaired growth in the studies reviewed"],"clashes":[],"sources":[{"id":"garlick2006","url":"https://europepmc.org/article/MED/16702346","label":"Toxicity of methionine in humans (Garlick PJ, J Nutr 2006; PMID 16702346)","quote":"Nutritional and metabolic studies have employed amounts of methionine … both below and above the requirement and have not reported adverse effects in adults and children … intakes higher than 5 times normal resulted in elevated homocysteine levels","accessed":"2026-08-27"},{"id":"garlick2006_death","url":"https://europepmc.org/article/MED/16702346","label":"Toxicity of methionine in humans (Garlick PJ, J Nutr 2006) — loading dose and overdose","quote":"A \"loading dose\" of methionine (0.1 g/kg) has been given … However, a 10-fold larger dose, given mistakenly, resulted in death.","accessed":"2026-08-27"},{"id":"garlick2006_schiz","url":"https://europepmc.org/article/MED/16702346","label":"Toxicity of methionine in humans (Garlick PJ, J Nutr 2006) — psychiatric effects","quote":"Although methionine is known to exacerbate psychopathological symptoms in schizophrenic patients, there is no evidence of similar effects in healthy subjects.","accessed":"2026-08-27"},{"id":"garlick2006_bvit","url":"https://europepmc.org/article/MED/16702346","label":"Toxicity of methionine in humans (Garlick PJ, J Nutr 2006) — B vitamin moderation","quote":"These effects of methionine on homocysteine and vascular function are moderated by supplements of vitamins B-6, B-12, C, and folic acid.","accessed":"2026-08-27"},{"id":"garlick2006_hcy","url":"https://europepmc.org/article/MED/16702346","label":"Toxicity of methionine in humans (Garlick PJ, J Nutr 2006) — main concern","quote":"The role of methionine as a precursor of homocysteine is the most notable cause for concern.","accessed":"2026-08-27"},{"id":"garlick2006_infants","url":"https://europepmc.org/article/MED/16702346","label":"Toxicity of methionine in humans (Garlick PJ, J Nutr 2006) — infants","quote":"In infants, methionine intakes of 2-5 times normal resulted in impaired growth and extremely high plasma methionine levels, but no adverse long-term consequences were observed.","accessed":"2026-08-27"},{"id":"elango2020","url":"https://europepmc.org/article/MED/33000159","label":"Methionine Nutrition and Metabolism: Insights from Animal Studies to Inform Human Nutrition (Elango R, J Nutr 2020; PMID 33000159)","quote":"Methionine is a nutritionally indispensable amino acid, and is unique among indispensable amino acids due to its sulfur atom.","accessed":"2026-08-27"},{"id":"elango2020_fn","url":"https://europepmc.org/article/MED/33000159","label":"Methionine Nutrition and Metabolism (Elango R, J Nutr 2020) — functions","quote":"Methionine is involved in cysteine synthesis via the transsulfuration pathway, which is rate limiting for the key antioxidant molecule, glutathione. Methionine is also the primary methyl donor in the body","accessed":"2026-08-27"},{"id":"paoletti2023","url":"https://europepmc.org/article/PMC/PMC10574673","label":"The Minimum Methionine Requirement for Adults Aged >=60 Years Is the Same in Males and Females (Paoletti et al., Nutrients 2023; PMC10574673)","quote":"the data were pooled to generate a mean of 5.1 mg/kg/d … This is the first study to estimate the minimum methionine requirement in healthy older adults","accessed":"2026-08-27"},{"id":"hsa_hs_defn","url":"https://file.go.gov.sg/hsa-hs-guidelines.pdf","label":"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)","quote":"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.","accessed":"2026-08-27"},{"id":"hsa_pr_notlisted","url":"https://file.go.gov.sg/hsa-chp-prohibited-restricted-ing-guidelines.pdf","label":"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 methionine","quote":"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.","accessed":"2026-08-27"},{"id":"iherb_sg","url":"https://sg.iherb.com/c/l-methionine","label":"iHerb Singapore category page \"L-Methionine: Essential Amino Acid for Liver Support\", default best-selling order, first 5 distinct brands","quote":"L-Methionine: Essential Amino Acid for Liver Support","accessed":"2026-08-27"}],"brand_certs":null,"updated_at":"2026-08-29T16:16:24.715168+08:00"},"disclaimer":"kozen-x is not a medical device and does not give medical advice. it lists what published sources have written down. absence of a record is not the same as safe."}