Methionine is one of nine essential amino acids, so called because they cannot be made by the human body and must be obtained through the diet. Sources of methionine include protein-rich foods such as beef, chicken, fish, liver, pork, cottage cheese, eggs, lentils, pumpkin seeds, sesame seeds, sunflower seeds, and yogurt.
Supplementary L-methionine has been used to treat symptoms of Parkinson's disease, insomnia, and severe acetaminophen (e.g., Tylenol®) poisoning. In addition, increased dietary intake of methionine has been shown to reduce the risk of a specific type of brain and spinal cord birth defect known as neural tube defects (NTDs). More well-designed human studies are needed to determine if methionine is safe and effective for treating any medical condition.
Very high doses of supplementary methionine have been shown to increase levels of the amino acid homocysteine. High homocysteine levels are a risk factor for heart disease. Some studies have suggested links between methionine and cancer, but more research is needed before firm conclusions can be made.

Related Terms

Amino acid, butanoic acid, C5H11NO2S, D-methionine, essential amino acid, L-methionine, M, Met, metioniini (Finnish), methionin (Czech, Danish), Methionin (German), metionin (Czech, Danish, Faroese, Norwegian, Swedish), metionín (Slovenian), metionina (Hungarian, Italian, Polish, Portuguese, Spanish), méthionine (French), nonpolar amino acid, S-adensyl-L- methionine (SAMe).

evidence table

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Acetaminophen toxicity (Grade: C)
Several studies have investigated the use of methionine for treatment of acetaminophen (e.g., Tylenol®) overdose. In a study of patients with acetaminophen poisoning, methionine worked as well as standard treatment with acetylcysteine in preventing major liver damage and death. Further study is required before any conclusion can be made.
Insomnia (Grade: C)
A small, preliminary human study showed that L-methionine may help relieve chronic insomnia in AIDS patients. Additional research on methionine as a therapy for insomnia is needed.
Neural-tube defect prevention (brain and spinal cord birth defect prevention) (Grade: C)
Results of a human study revealed a lower risk of neural tube defects (birth defects of the brain and spinal cord) in the fetuses of women who had relatively higher dietary intake of methionine near the time that they became pregnant. Additional research is needed to investigate the roles of dietary and supplemental methionine in reducing this type of birth defect.
Parkinson's disease (Grade: C)
Supplementary methionine helped reduce some clinical symptoms of Parkinson's disease in a small human study. More high quality studies are needed to clearly determine the effectiveness of methionine in the treatment of Parkinson's symptoms.