Methionine
EVIDENCE: WEAKAlso sold as: L-methionine, Met, dl-methionine
Methionine is an essential amino acid used to build proteins and make compounds including SAMe and glutathione. It must come from the diet. Additional supplementation has no established general treatment role, and high doses can raise homocysteine.
Compiled by iSupplementReviews editorial team ·Updated 2026-10-06 · 3 sources
- Type
- Essential amino acid
- Studied dose
- Dietary requirement ~13–16 mg/kg/day; supplement doses studied 1–10 g+ (mostly for urinary acidification or research use)
- Best form
- Dietary protein covers it (eggs, fish, sesame, brazil nuts); supplementation is rarely necessary for omnivores
- Upper limit
- No formal upper intake limit — high intakes raise homocysteine (cardiovascular marker); toxic in grams at extremes
- Our rating
- WEAK — Mostly small, animal, or traditional evidence
What is methionine?
Methionine is an essential sulfur-containing amino acid used in protein synthesis. It is also involved in making SAMe, cysteine, and glutathione. Ordinary dietary protein supplies it, so its essential role does not establish a need for extra supplementation.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Essential nutrient status | Established nutrition science | ~13–16 mg/kg/day | Settled — dietary |
| SAMe/glutathione precursor | Established biochemistry | — | Settled — mechanism |
| Urinary acidification | Clinical use (pH lowering) | gram doses | Niche, medical |
| Health benefit from extra intake | No evidence of benefit in replete adults | — | Unproven |
| Homocysteine lowering | Opposite — raises it | — | Counter-evidence |
What dose was studied?
The requirement is ~13–16 mg/kg/day total (methionine + cysteine combined); adults eating normal protein exceed this comfortably. High-dose gram regimens exist in research and medical contexts (urinary acidification, animal studies), none supporting routine supplementation.
Side effects
At blend-level doses, none. At gram doses: digestive upset, and the documented risk of elevated homocysteine, a cardiovascular-risk marker. Methionine is the amino acid where ‘more’ actively trends wrong.
Drug interactions
- Levodopa: high amino-acid intake can affect Parkinson’s medication handling.
- MAOIs/stimulants: theoretical via methylation pathways; not a demonstrated clinical interaction at supplement doses.
Who should not take it
People with homocystinuria or elevated homocysteine, liver failure (methionine-load intolerance), or schizophrenia-spectrum disorders at high doses (excess methylation can worsen symptoms). Anyone already eating adequate protein gains nothing.
What the authorities say
National Academies DRI tables set the requirement and note that typical Western diets provide ample methionine; no authority recommends supplementation for omnivores.
What to know about methionine
Additional methionine has no established general benefit for people with adequate protein intake. High amounts can raise homocysteine. Its biochemical importance should not be confused with proof of a supplement treatment effect.
Frequently asked questions about Methionine
Do I need to supplement methionine?
Almost certainly not if you eat protein. Eggs, fish, meat, sesame seeds, and brazil nuts are rich in it. It's an essential amino acid, not a deficiency-prone one for omnivores. The people who might run low are strict vegans on grain-only diets, and they fix it with protein variety, not capsules.
What does methionine do in the body?
Methionine helps the body make SAMe, which transfers methyl groups in reactions involving DNA and neurotransmitters. It also contributes to the production of cysteine and glutathione. These essential roles do not show that a small supplemental amount provides an extra benefit.
Why would a dental supplement contain methionine?
Human research has not established a dental benefit. Methionine contributes to proteins and tissue maintenance, but most people eating adequate protein already obtain it from food. That role does not demonstrate an effect from tens of milligrams in a dental blend.
Is too much methionine bad?
Yes; this is a nutrient where more isn't better. High methionine intake raises homocysteine (a cardiovascular-risk marker), animal studies link excess to vascular effects, and gram-level chronic dosing has no safety case for healthy people. A 50-ish mg blend line is harmless, but also pointless.
Methionine vs SAMe — same thing?
No. SAMe is what the body MAKES from methionine, and it's the version with actual mood and joint trials (at 400–1600 mg/day). Plain methionine is the raw material, not the active: you can't infer SAMe benefits from methionine supplementation.