L-Methionine
An essential amino acid central to methylation. There is no trial showing a benefit from supplementing it in healthy, protein-fed people, and loading doses measurably raise homocysteine.
Evidence last reviewed: August 2026
What the science says
- Extra methionine raises homocysteine Moderate evidence
Controlled human studies using oral methionine loading show that it acutely raises plasma homocysteine and transiently impairs endothelial function in healthy volunteers. This is the standard method for inducing experimental hyperhomocysteinaemia, which makes it an argument against casual supplementation rather than for it.
- Antidote use, not supplement use Moderate evidence
Oral methionine has a place in medicine as a second-line antidote in paracetamol overdose, covered in a Cochrane review of interventions for paracetamol poisoning, where intravenous acetylcysteine remains the preferred treatment. That clinical niche says nothing about taking methionine daily for liver support.
- Methionine intake and metabolic health Limited evidence
A review of sulfur amino acids and metabolic health notes that the experimental direction of interest is currently methionine restriction rather than supplementation, with human evidence still preliminary in both directions.
Dosage & safety
Scientific references
- Relationship between S-adenosylmethionine, S-adenosylhomocysteine, asymmetric dimethylarginine, and endothelial function in healthy human subjects during experimental hyper- and hypohomocysteinemia
- Interventions for paracetamol (acetaminophen) overdose
- Sulfur amino acids, metabolic health and beyond: Recent advances, translational implications, and future research considerations
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