Amino Acid ·Moderate evidence ·Reviewed May 2026
Essential sulfur-containing amino acid, precursor to SAMe and cysteine.
The bottom line
Evidence rating moderate. Most-documented uses: methylation, detoxification, joint health. 17 sources indexed (1989–2024), with 4 interaction records on file.
Core mechanism
Activated by methionine adenosyltransferase to SAMe. Enters transmethylation (SAMe→SAH), transsulfuration (cysteine→glutathione), and polyamine synthesis pathways.1,11
Dosing protocol
Pair with adequate B12, folate, B6 to manage homocysteine. Avoid in homocystinuria.
Ranked by evidence and value.
Real-world pricing across three quality tiers. Assumes L-Methionine Free Form.
Assumes 500-1,500 mg/day. Vendor basis: NOW/iHerb, Vitacost, BulkSupplements powder, and Amazon marketplace; capsules cost more than powder. Updated 2026-05-28.
How much you'd eat to match a supplemental dose.
Whole foods supply methionine with other amino acids and micronutrients.
What to test, the optimal window inside the conventional range, and how long a response takes.
L-methionine loading raises homocysteine in B-vitamin-insufficient states; in adequate states, methionine is recycled efficiently.9,13
Always interpret homocysteine alongside B12, folate, and B6. Methionine load test is rarely used clinically now.
Methionine is recycled from homocysteine via B12-dependent methionine synthase; adequate B12 is required to handle methionine load without raising homocysteine.
Recommendation: Pair methionine supplementation with adequate B12, folate, and B6. Test homocysteine to confirm methylation is supported.
Methylfolate is the methyl donor that enables homocysteine remethylation to methionine via methionine synthase.
Recommendation: Always pair methionine with adequate methylfolate (and B12) to manage homocysteine.
Vitamin B6 is the obligate cofactor for the transsulfuration enzymes that clear the homocysteine generated when L-Methionine is metabolized. In humans, methionine loading produces a sharper homocysteine spike when B6 status is low, and B6 supplementation measurably blunts that spike. Pairing supplemental methionine with adequate B6 directs the homocysteine pool toward cysteine and glutathione synthesis rather than letting it accumulate.
Recommendation: If supplementing L-Methionine regularly or at higher doses, ensure adequate Vitamin B6 status. A practical co-dose is roughly 10 to 25 mg/day of B6 (as pyridoxine or P5P) taken with meals. Do not exceed about 100 mg/day of supplemental B6 long term due to neuropathy risk. They can be taken together; no timing separation is needed. Those with elevated homocysteine should also confirm folate and B12 status, since remethylation runs in parallel.
Glycine is the acceptor substrate for GNMT, a main enzyme that buffers excess methylation potential created when L-Methionine raises SAMe. Adequate glycine helps dissipate surplus methyl groups and has been reported to lower homocysteine in high-methionine or high-protein conditions. The relationship is a complementary methyl-disposal pathway rather than a risk.
Recommendation: No avoidance needed; this is a supportive pairing. If using L-Methionine alongside a higher-protein or methylation-supportive regimen, ordinary dietary or supplemental glycine (commonly 3 to 5 g/day) is sufficient to support methyl-group disposal. They can be taken together or at different times of day with no required separation.
Numbered references. Citations throughout the page link here.
Limveeraprajak N, Nakhawatchana S, Visukamol A et al.. Efficacy and acceptability of S-adenosyl-L-methionine (SAMe) for depressed patients: A systematic review and meta- analysis. Progress in neuro-psychopharmacology & biological psychiatry. 2024
Dondi F, Gazzilli M, Viganò GL et al.. The Role of 11C-Methionine PET Imaging for the Evaluation of Lymphomas: A Systematic Review. Hematology reports. 2024
Roufael M, Bitar T, Sacre Y et al.. Folate-Methionine Cycle Disruptions in ASD Patients and Possible Interventions: A Systematic Review. Genes. 2023
Souza VC, Remus A, Batonon-Alavo DI et al.. Systematic review and meta-analysis of the methionine utilization efficiency in piglets receiving different methionine sources. Animal : an international journal of animal bioscience. 2023
Wei C, He T, Wan X et al.. Meta-Analysis of Rumen-Protected Methionine in Milk Production and Composition of Dairy Cows. Animals : an open access journal from MDPI. 2022
Wei DH, Mao QQ. Vitamin B6, vitamin B12 and methionine and risk of pancreatic cancer: a meta-analysis. Nutrition journal. 2020
Raikhelson KL, Kondrashina EA. Аdеmethionine in the treatment of fatigue in liver diseases: a systematic review. Terapevticheskii arkhiv. 2019
Katsanos AH, Alexiou GA, Fotopoulos AD et al.. Performance of 18F-FDG, 11C-Methionine, and 18F-FET PET for Glioma Grading: A Meta-analysis. Clinical nuclear medicine. 2019
Supplementation of 1500 mg L-methionine daily significantly increased homocysteine plasma concentrations by 2.0 micromol/l despite adequate vitamin status.
SAMe therapy resulted in a significant increase in hepatic glutathione levels in patients with both alcoholic and non-alcoholic liver diseases.
Methionine restriction and supplementation both provide promising outcomes; its regulation is critical for maintaining health, but excess intake without B vitamins may cause hyperhomocysteinemia.
Methionine is the precursor of homocysteine; deficient B vitamin intake or excessive methionine intake may result in hyperhomocysteinemia, a cardiovascular risk factor.
Up to half of the daily methionine intake is catabolized to SAMe in the liver; the transsulfuration pathway allows methionine to serve as a glutathione precursor.
Hepatocytes incubated with methionine showed increased intracellular glutathione with a twofold increase observed on day 6, supporting methionine's role in detoxification.
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