L-Methionine
Also known as: methionine, L-Met
Randomized human trials show L‑methionine supplementation can increase plasma methionine and related metabolites and can improve nitrogen balance when added to a methionine‑poor diet. In children with severe acute malnutrition methionine increased cysteine flux from body protein but did not increase erythrocyte glutathione synthesis. Daily supplementation (1.5 g/day) raises plasma homocysteine modestly.
Last reviewed: 2026-10-14 · 3 indexed studies
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Overview
L‑Methionine is an essential sulphur-containing amino acid used to supply dietary sulphur amino acids and to improve the amino acid profile of low-methionine foods. Human trials have evaluated its effects on nitrogen balance, cysteine and glutathione metabolism in malnutrition, and on plasma homocysteine when given orally.
Mechanism & Function
Mechanism of Action
L‑Methionine serves as an essential amino acid and a methyl group donor after conversion to S‑adenosylmethionine; it is a precursor for homocysteine and, via the transsulphuration pathway, for cysteine which can contribute to glutathione synthesis.
Physiological Role
Dietary source of sulphur amino acids, precursor for methylation reactions, and substrate for cysteine and glutathione synthesis.
Primary Pathways
Performance / Health Relevance
By supplying an essential sulphur amino acid, L‑methionine can improve nitrogen balance on methionine‑limited diets and increase availability of downstream metabolites (cysteine, cystathionine), which may be relevant for protein synthesis and antioxidant substrate availability; however, evidence does not show increased glutathione synthesis in malnourished children and supplementation raises homocysteine.
Evidence Review
No meta-analyses or systematic reviews indexed for this ingredient yet.
Dimensions marked N/A have no indexed evidence of that class. They are shown as unavailable rather than scored.
Practical Use & Dosage
- Minimum Effective Dose
- Not established for general use; studied doses include ~1.5 g/day in adults and 0.5 mmol·kg⁻¹·day⁻¹ in children with severe malnutrition (used in the cited trial).
- Optimal Range
- Not established.
- Upper / Caution Level
- Not established; caution due to reproducible increases in plasma homocysteine at studied doses.
- Timing
- Not established.
- Best Format
- Oral tablet or powder as L‑methionine.
- Bioavailability
- Oral L‑methionine is absorbed and increases plasma methionine and downstream metabolites.
- Absorption Considerations
- Competes with other large neutral amino acids for transport; dietary protein context may affect utilisation.
Safety & Interactions
Side Effects
- •Increase in plasma homocysteine concentrations
- •Increased renal excretion of methionine and homocysteine reported
Contraindications
- Known hyperhomocysteinaemia or uncontrolled cardiovascular disease (caution because supplementation increases homocysteine)
Drug Interactions
- •None established in the provided abstracts; consider interactions where altered methylation/homocysteine may be relevant
Who Should Avoid
- •People with elevated cardiovascular risk related to homocysteine
- •Those not taking adequate B‑vitamin (folate/B6/B12) supplementation if using methionine
Monitoring
Consider monitoring plasma homocysteine when using supplemental L‑methionine, especially at gram‑level daily intakes; ensure adequate folate/B6/B12 status to support homocysteine remethylation/transsulphuration.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is L-Methionine typically used or indicated?
L-Methionine is most commonly used for: Support dietary sulphur amino acid intake, Improve protein quality of low-methionine diets, Support glutathione/cysteine precursor status (theoretical). Dietary source of sulphur amino acids, precursor for methylation reactions, and substrate for cysteine and glutathione synthesis.
How does L-Methionine work?
L‑Methionine serves as an essential amino acid and a methyl group donor after conversion to S‑adenosylmethionine; it is a precursor for homocysteine and, via the transsulphuration pathway, for cysteine which can contribute to glutathione synthesis.
What is the recommended dose of L-Methionine?
The optimal range is Not established.. with a minimum effective dose of Not established for general use; studied doses include ~1.5 g/day in adults and 0.5 mmol·kg⁻¹·day⁻¹ in children with severe malnutrition (used in the cited trial).. Best taken: Not established.. Upper / caution level: Not established; caution due to reproducible increases in plasma homocysteine at studied doses..
What are the side effects of L-Methionine?
Reported side effects include: Increase in plasma homocysteine concentrations; and Increased renal excretion of methionine and homocysteine reported. Monitoring: Consider monitoring plasma homocysteine when using supplemental L‑methionine, especially at gram‑level daily intakes; ensure adequate folate/B6/B12 status to support homocysteine remethylation/transsulphuration.
Does L-Methionine interact with medications?
Known or theoretical interactions: None established in the provided abstracts; consider interactions where altered methylation/homocysteine may be relevant. Always check with a clinician before combining with prescription medication.
Who should avoid L-Methionine?
L-Methionine is generally not recommended for: People with elevated cardiovascular risk related to homocysteine; Those not taking adequate B‑vitamin (folate/B6/B12) supplementation if using methionine; and Known hyperhomocysteinaemia or uncontrolled cardiovascular disease (caution because supplementation increases homocysteine).
How strong is the evidence for L-Methionine?
Evidence level: Limited (overall score 46/100), based on 3 indexed studies on SuppIndex.
Research & References (3)
Effects of randomized supplementation of methionine or alanine on cysteine and glutathione production during the early phase of treatment of children with edematous malnutrition.
Randomized supplementation of methionine (0.5 mmol·kg⁻¹·day⁻¹) versus alanine in 12 children with edematous severe acute malnutrition. Methionine increased cysteine flux derived from body protein and raised plasma cysteine changes between early phases, but did not change cysteine de novo synthesis, total cysteine flux, or erythrocyte glutathione synthesis rate or concentration.
Comparative value of L-, and D-methionine supplementation of an oat-based diet for humans.
Randomized study comparing L‑, DL‑ and D‑methionine supplementation of an oat‑based diet in adult subjects. L‑methionine supplementation improved nitrogen balance compared with unsupplemented diet, whereas D‑methionine was poorly utilised.
Effect of L-methionine supplementation on plasma homocysteine and other free amino acids: a placebo-controlled double-blind cross-over study.
Placebo‑controlled double‑blind cross‑over study in 20 women (8 with chronic UTI, 12 healthy) given 500 mg L‑methionine three times daily for 4 weeks. L‑methionine supplementation increased serum methionine, cystathionine and plasma homocysteine concentrations and increased urinary excretion of methionine and homocysteine.
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Research Overview
Limited EvidenceCite this ingredient
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Stable URL
https://thesuppindex.com/ingredients/l-methionine
SuppIndex. (2026). L-Methionine: Evidence summary, dosage and clinical studies. Retrieved October 16, 2026, from https://thesuppindex.com/ingredients/l-methionine
Based on 3 indexed studies · Evidence level: Limited.
Goal Ratings
Stack Compatibility
Co‑supplementation with folate, vitamin B6 and B12 may mitigate methionine‑induced increases in homocysteine (suggested in the clinical trial).