Alternate Title

  • L-methionine

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).


  • 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.

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

    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.


    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)

    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

    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.

*Key to grades:



    The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.



    The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.

  • Adults (18 years and older)

    • The dietary reference intake recommendation for methionine and cysteine combined is 25 milligrams per gram of protein.
    • For acetaminophen (e.g., Tylenol®) toxicity, 2.5 grams of methionine has been taken by mouth every four hours for four doses with good results when given within 10 hours after acetaminophen use.
    • For insomnia, 500 milligrams of methionine has been taken by mouth just before bedtime.
    • For Parkinson’s disease, 5 grams of methionine has been taken by mouth daily for two weeks to six months.
  • Children (under 18 years old)

    • There is no proven safe or effective dose of methionine in children.



    The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.

  • Allergies

    • Because methionine is an essential amino acid, hypersensitivity and allergy are unlikely.
  • Side Effects and Warnings

    • Methionine may cause increased blood concentrations of homocysteine, decrease in bile flow, and liver injury.
    • Use cautiously in individuals taking gastrointestinal agents.
    • Use cautiously in patients who have or are at risk for elevated homocysteine levels or who are using agents that may elevate homocysteine levels (e.g., antiseizure agents, fenofibrate, niacin).
    • Use cautiously in infants receiving parenteral (put into the body other than via the digestive tract) nutrition with methionine, particularly in large amounts, due to increased risk of liver injury.
    • Use cautiously in individuals with liver disease or those who are taking drugs, herbs, or supplements that may damage the liver.
    • Avoid large amounts of methionine (more than 100 milligrams per kilogram of body weight), as it may lead to severe brain effects.
  • Pregnancy and Breastfeeding

    • Studies have shown that methionine contributes to the normal formation of the brain and spinal cord during pregnancy. Low levels of methionine during pregnancy may be, in part, responsible for a specific class of brain and spinal cord birth defects known as neural tube defects (NTDs). A methionine-rich diet during pregnancy may help prevent neural tube defects. Further study is needed.
    • Supplemental methionine is not indicated in breastfeeding women due to a lack of available scientific evidence.



    Most herbs and supplements have not been thoroughly tested for interactions with other herbs, supplements, drugs, or foods. The interactions listed below are based on reports in scientific publications, laboratory experiments, or traditional use. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy.

  • Interactions with Drugs

    • Methionine may interact with anticancer agents (including cisplatin and 5-fluorouracil), agents that elevate homocysteine levels (including fenofibrate, niacin, metformin, antiseizure drugs, levodopa, and methotrexate), and agents that may damage the liver.
  • Interactions with Herbs and Dietary Supplements

    • Methionine may interact with anticancer herbs and supplements, foods containing large amounts of methionine (such as red meat and chicken), herbs and supplements that elevate homocysteine levels, and herbs and supplements that may damage the liver.


  • This information is based on a systematic review of scientific literature edited and peer-reviewed by contributors to the Natural Standard Research Collaboration ().



    Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to . Selected references are listed below.

  • Btaiche IF and Khalidi N. Parenteral nutrition-associated liver complications in children. Pharmacotherapy 2002;22(2):188-211.
    View Abstract
  • Cagnacci A, Generali M, Pirillo D, et al. Effects of low- or high-dose hormone therapy on fasting and post-methionine homocysteine levels in postmenopausal women. Climacteric 2006;9(5):388-95.
    View Abstract
  • Cellarier E, Durando X, Vasson MP, et al. Methionine dependency and cancer treatment. Cancer Treat.Rev 2003;29(6):489-499.
    View Abstract
  • Cottington EM, LaMantia C, Stabler SP, et al. Adverse event associated with methionine loading test: a case report. Arterioscler Thromb Vasc Biol 2002;22(6):1046-1050.
    View Abstract
  • Epner, DE. Can dietary methionine restriction increase the effectiveness of chemotherapy in treatment of advanced cancer? J Am Coll Nutr 2001;20(5 Suppl):443S-449S.
    View Abstract
  • Hamlyn AN, Lesna M, Record CO, et al. Methionine and cysteamine in paracetamol (acetaminophen) overdose, prospective controlled trial of early therapy. J Int Med Res 1981;9(3):226-231.
    View Abstract
  • Hanratty CG, McGrath LT, McAuley DF, et al. The effects of oral methionine and homocysteine on endothelial function. Heart 2001;85(3):326-330.
    View Abstract
  • Larsson SC, Giovannucci E, Wolk A. Methionine and vitamin B6 intake and risk of pancreatic cancer: a prospective study of Swedish women and men. Gastroenterology 2007;132(1):113-118.
    View Abstract
  • Moss RL, Haynes AL, Pastuszyn A, et al. Methionine infusion reproduces liver injury of parenteral nutrition cholestasis. Pediatr Res 1999;45(5 Pt 1):664-668.
    View Abstract
  • Shaw GM, Velie EM, Schaffer DM. Is dietary intake of methionine associated with a reduction in risk for neural tube defect-affected pregnancies? Teratology 1997;56(5):295-299.
    View Abstract
  • Shoob HD, Sargent RG, Thompson SJ, et al. Dietary methionine is involved in the etiology of neural tube defect-affected pregnancies in humans. J Nutr 2001;131(10):2653-2658.
    View Abstract
  • Tan Y, Zavala J Sr, Xu M, et al. Serum methionine depletion without side effects by methioninase in metastatic breast cancer patients. Anticancer Res 1996;16(6C):3937-3942.
    View Abstract
  • Trumbo P, Schlicker S, Yates AA, et al. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein and amino acids. J Am Diet Assoc 2002;102(11):1621-1630.
    View Abstract
  • Van Brummelen R, du Toit D. L-methionine as immune supportive supplement: a clinical evaluation. Amino Acids 2007;33(1):157-63.
    View Abstract
  • Ward M, McNulty H, McPartlin J, et al. Effect of supplemental methionine on plasma homocysteine concentrations in healthy men: a preliminary study. Int J Vitam Nutr Res 2001;71(1):82-86.
    View Abstract