An essential sulphur-containing amino acid and the starting point for the body's main methyl donor. Rarely deficient in anyone eating protein, and one of the few amino acids where more is not obviously better.
Typical dose
500.0–1000.0 mg per day
With food, if used
What it is
L-methionine is one of the nine essential amino acids and one of only two containing sulphur, the other being cysteine. It is abundant in eggs, fish, meat, dairy and Brazil nuts, and lower in most plant proteins, with legumes particularly limited in it.
Its most important role is as the precursor to S-adenosylmethionine, or SAMe, the body's principal methyl donor. Methylation is involved in DNA regulation, neurotransmitter synthesis, detoxification and the production of creatine, carnitine and phosphatidylcholine.
Methionine is also the amino acid every protein starts with during synthesis, and it feeds the transsulphuration pathway that produces cysteine and, downstream, glutathione. Deficiency in anyone eating adequate protein is essentially unheard of, which shapes how useful supplementation is likely to be.
How it works
Methionine is converted to SAMe, which donates its methyl group to hundreds of reactions and in doing so becomes homocysteine. Homocysteine is then either recycled back to methionine, using folate and vitamin B12, or converted onward to cysteine using vitamin B6.
That cycle explains both the value and the caution. Adequate methionine supports methylation capacity; excess methionine without sufficient B vitamins raises homocysteine, which is not something to invite.
Methionine also contributes to glutathione production via the transsulphuration route. Betaine, folate and B12 all support recycling homocysteine back to methionine, which is why these nutrients are frequently discussed together.
What the evidence shows
There is little evidence supporting methionine supplementation in healthy, well-fed people, and no established performance or body composition benefit. This is an amino acid whose importance in physiology far exceeds its usefulness as a supplement.
It has a small number of supervised medical applications, but those are administered under supervision and are not a supplement use.
An interesting research strand runs the other way. Methionine restriction has been studied for metabolic and longevity outcomes in animal models, with generally favourable findings. That literature is preliminary and does not translate into advice for humans, but it is a reminder that more is not automatically better here.
Dosing
Supplemental doses, where used at all, are typically 500-1,000 mg daily. Ordinary dietary intake in an omnivorous diet is already several grams daily.
If taking supplemental methionine for any reason, adequate folate, vitamin B12 and vitamin B6 status matters, since these are what allow homocysteine produced downstream to be recycled or cleared. Taking methionine without them is the scenario where homocysteine rises.
For most people eating adequate protein, there is no clear reason to supplement it. Where the underlying goal is glutathione support, NAC is the more sensible and better-evidenced route.
At a glance
Common forms
L-methionine capsules, L-methionine powder, SAMe (downstream metabolite), Within EAA blends
Half-life / duration
Plasma methionine peaks within 1-2 hours
Timing
With food, if used
Competition status
Permitted — not on the WADA Prohibited List
Category
Foundational
Safety and side effects
At intakes from food, methionine is entirely safe. Supplemental doses are generally tolerated, with nausea, drowsiness and irritability reported occasionally.
The main consideration is homocysteine. High methionine loading raises it, particularly where folate, B12 or B6 status is inadequate, and raised homocysteine is not something to invite. This is the reason to be conservative with supplemental doses rather than assuming more is better.
Anyone who has been told their liver is not working normally should avoid supplemental methionine, and anyone advised to restrict specific amino acids in their diet should avoid it entirely.
Who should avoid it
Avoid if you have been advised to restrict specific amino acids in your diet. Avoid if you have been told your liver is not working normally. Ensure adequate folate, B12 and B6 status if supplementing. Speak to your doctor before use if you take regular medication or are under medical care. Not established for use in pregnancy or breastfeeding at supplemental doses.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
