|See Also||Amino Acids|
Methionine is an essential amino acid which is intimately involved in the homocysteine metabolism pathway. Homocysteine is an intermediate metabolite that results during the conversion of methionine to cysteine. How much homocysteine is present in the blood is directly related to how much methionine is taken in through food and how much is metabolized. Adequate intake of folic acid, vitamin B12, vitamin B6, and betaine are all necessary to ensure proper recycling of methionine such that homocysteine levels do not elevate..
The following foods have the highest concentration of methionine:
- Richest Dietary Sources: dairy products, fish, beef, chicken, pork, liver
- Good Sources: sunflower seeds, pumpkin seeds, sesame seeds, lentils
Methionine has many important functions in the body.
- It is important for the translation of messenger RNA.
- It is converted into S-adenosylmethionine (SAMe) which is considered the active form of methionine. SAMe is important for the manufacturing of many brain chemicals and detoxification reactions. SAMe is also an important methyl donor.
- It is a lipotropic factor meaning that it is involved in fat metabolism.
- It is an important source of sulfur for various functions in the body that are essential for liver detox and the synthesis of many amino acids (including cysteine, proteins, and enzymes. It is the precursor for the amino acids cysteine and taurine: it is one of three amino acids which make up creatine and is a precursor to glutathione which is a crucial antioxidant .
- It enhances liver function, detoxification, and lipid metabolism.
- It support the function of the Central Nervous System.
Typical symptoms of methionine deficiency include: 
- hair loss
- hepatic dysfunction
- poor skin tone
- toxic elevation of metabolic waste products
- Lower methionine levels in pregnancy have been associated with neural tube defects.
Methionine deficiency is usually associated with an overall protein deficiency.
Signs of methionine toxicity include:
- nausea and gastrointestinal irritation
- reduced growth
- suppressed hematocrit
- extremely high doses may induce hallucinations.
- L-methionine supplements should only be taken with a physician's recommendation.
- Methionine is available in capsules, powder, and tablets.
- No RDA established. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- General Adverse Effects: Some sensitive individuals may experience gas, gas/bloating, and digestive discomfort during supplementation as low as 500mg/day.
- Contraindications: Avoid SAMe in Parkinson's disease due to a potential aggravation of symptoms.
- Precautions: Large intakes of methionine require higher intakes of methyl donor-related nutrients such as vitamin B12, folic acid, vitamin B6, choline, betaine and others. Without these additional nutrients, homocysteine levels can increase in the blood. Supplementation may be inappropriate for individuals with osteoporosis because it can increase urinary excretion of calcium.
Drug interactions include:
- Supportive or Beneficial:
- Acetaminophen - Methionine appears to reduce the toxic effects of the drug, especially on the liver. Co-administer within the same dose.
- Levodopa (L-dopa) - Methionine at lower doses can benefit those with Parkinson's disease, but at higher doses may interfere with the action of the drug. Co-administration of folic acid, vitamin B12, and vitamin B6 important. Monitor for interference with drug.
Nutrient interactions include: 
- Pizzorno Joseph E, Murray Michael T (2005) Textbook of Natural Medicine, Elsevier
- Stargrove Mitchell Bebell, Treasure Jonathan, McKee Dwight L (2008) Herb, Nutrient, and Drug Interactions, Clinical Implications and Therapeutic Strategies Mosby