L-Methionine

Methionine

Snapshot

Indications	Contraindications
Chronic liver disease¹ Telogen effluvium^{2, 3} Androgenetic alopecia³ Methionine synthase deficiency⁴	Pregnancy or lactation⁵ Under 18 years⁵

L-Methionine is an essential sulfur-containing amino acid required for protein synthesis⁶. It is the precursor of glutathione and of the body's main methyl donor, S-adenosylmethionine (SAMe).¹ Supplementation is used to support these methylation and glutathione pathways, particularly in chronic liver disease. It also appears with other sulfur amino acids in oral hair-loss formulas for telogen effluvium and androgenetic alopecia, where combination-product trials are small³.

Low plasma methionine tracked with 30-day mortality in nutritionally at-risk inpatients⁷. A review reports that adequate supplementation may reduce liver damage, largely from preclinical work¹. In mouse tumor and infection models, a 2025 study found brief early methionine supplementation augmented antitumor T cell activity; no human trial has tested it. Products listing L-methionine are mostly single-ingredient capsules with a few powders; see Form comparison.

The main concern is homocysteine, which methionine produces.⁸ An oral load impaired endothelium-dependent vasodilation in healthy adults, a change attributed to homocysteine rather than methionine⁸. Plasma homocysteine rose at the highest supplemented intake in healthy older adults⁶. United States product labels ask for practitioner consultation before use with kidney or liver disease or medications⁵.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

53 sources, 44 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources