What Is Methionine?

An Essential Amino Acid for Healthy Skin, Hair, Nails, and More

Methionine (L-methionine) is a nutritional supplement as well as an essential amino acid found in food. Methionine is required for normal growth and repair of body tissues; it cannot be made by the body, but must be obtained from the diet; thus, it is considered an “essential” amino acid. There are two types of methionine—L-methionine (which is naturally-occurring) and D-methionine. Each contains the same chemical make-up, but the molecules are mirror images. A mixture of the two is called DL-methionine.

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Methionine is a sulfur-containing amino acid that improves the tone and elasticity of the skin, promotes healthy hair and strengthens the nails. Methionine supplements are commonly taken to treat various infections and disorders, but there is limited scientific research to support the efficacy of the supplements for the treatment of diseases. However, methionine is thought to be effective in the treatment of Tylenol (acetaminophen) poisoning.

Also Known As

Other names for methionine include:

  • D-methionine
  • DL methionine
  • DL-methionine
  • L-2-amino-4-(methylthio) butyric acid

What Is Methionine Used For?

The sulfur in methionine provides the body with many potential health benefits. These may include:

  • Nourishing the hair, skin, and nails
  • Protecting the cells from pollutants
  • Facilitating the detoxifying process
  • Slowing down the aging process
  • Helping with the absorption of other nutrients (such as selenium and zinc)
  • Aiding in the excretion of heavy metals (such as lead and mercury) helping the body’s excretion process
  • Preventing excess fat buildup in the liver (by acting as a lipotropic agent—one that facilitates the breakdown of fats)
  • Lowering cholesterol levels by increasing lecithin production in the liver

Tylenol (Acetaminophen) Overdose

Taking an oral (by mouth) dose of methionine within 10 hours of Tylenol (acetaminophen) overdose has been used in treating acetaminophen poisoning. Methionine is thought to prevent the byproducts of acetaminophen from damaging the liver as a result of an overdose of Tylenol. However, other treatments are also used and methionine may not be the most effective.


Although some of the research is mixed regarding colon cancer and methionine, a 2013 meta-analysis reports, "This meta-analysis indicates that dietary methionine intake may be associated with decreased risk of colorectal cancer, especially colon cancer. More prospective studies with long follow-up time are needed to confirm these findings." For example, a 2016 study reported “Among the 10 essential amino acids tested, methionine deprivation elicited the strongest inhibitory effects on the migration and invasion of these [breast] cancer cells.”

Some studies show that a low methionine diet could be beneficial. There are specific types of cancer cells that depend on methionine to grow. Thus, limiting the intake of foods containing methionine is beneficial for those who have some types of cancer, because it results in the death of the cancer cells.

Alzheimer’s Disease

Studies suggest that L-methionine may help to improve memory and brain function, but according to a study published by Molecular Neurodegeneration, “Some evidence indicates that an excess of methionine can be harmful and can increase the risk of developing Type-2 diabetes, heart diseases, certain types of cancer, brain alterations such as schizophrenia, and memory impairment.”

Research on L-methionine and Alzheimer's disease has only been conducted in animal studies. In a 2015 mouse model study discovered that a diet enriched with L-methionine resulted in:

  • An increase in amyloid (a substance that commonly builds up in the brains of those with Alzheimer’s disease)
  • A rise in the level of tau protein in the brain (an increase can result in tau protein misfolding and clumping together to form abnormal tau tangles, found in those with Alzheimer’s)
  • An increase in oxidative stress and inflammatory response (both thought to raise the risk of Alzheimer’s disease)
  • Memory impairment and memory loss

The study authors concluded, “Taken together, the results of our study indicate that an L-methionine-enriched diet causes effects in [taking place in a living organism] and might contribute to the appearance of Alzheimer’s-like disease in wild-type animals."

Other Uses

Methionine is commonly taken for other disorders, but there is a lack of clinical research study results to back up the safety and efficacy of its use in these conditions:

  • Herpes simplex and herpes zoster (shingles)
  • Symptoms of menopause
  • Inflammation of the pancreas
  • Liver problems
  • Depression
  • Alcoholism
  • Urinary tract infections (UTI’s)
  • Asthma and allergies
  • Schizophrenia

Possible Side Effects

Methionine may cause several mild side effects, including nausea and vomiting, drowsiness and irritability. In fact, nausea is reportedly a very common side effect that can occur from taking methionine supplements.


A contraindication is a condition or circumstance indicating that a specific technique or drug should not be used. Methionine is contraindicated for those who have:

  • Liver damage
  • Hepatic encephalopathy (a decrease in the function of the brain caused by liver damage)
  • Severe liver disease (such as cirrhosis of the liver)
  • Acidosis (an excessive acid condition of the body and its the acidity of the blood)
  • Pregnancy and breastfeeding (there are not enough reliable data to support the safety of methionine for developing embryos or breastfeeding infants).
  • Atherosclerosis (hardening of the arteries): The nutritional supplement has been associated with an increased risk for heart disease, as methionine may increase homocysteine levels—high homocysteine is associated with poor cardiovascular outcomes.
  • Schizophrenia: Large doses of methionine (over 20 g per day for five days) have been known to cause confusion, delirium, and agitation in those with schizophrenia.
  • Methylenetetrahydrofolate reductase (MTHFR) deficiency (a hereditary disease involving an abnormal method of processing of risk of heart disease)

Dosage and Preparation

The Recommended Daily Allowance (RDA) for methionine (with another amino acid containing called cysteine) for adults is 14 mg/Kg of body weight each day. 

It’s important to consult with a healthcare provider regarding the dose and how long a person takes methionine supplements. Clinical research study results do not point to serious signs of toxicity, except at very high doses of methionine. Daily doses of 250 milligrams (mg), which is approximately 25% of the recommended daily dose of methionine, are reportedly safe.

The adult dosage of methionine for acetaminophen overdose is 2.5 grams every four hours (up to a total of 10 grams). As a Tylenol overdose can be fatal, it is essential to get emergency medical help rather than self-treating.

What to Look For

Select a product that provides potency, safety, and purity. A certified organic product, tested by a third party, such as the U.S. Pharmacopeia, NSF International, Consumer Lab, or Underwriters Laboratory is advisable. This is because unlike medications, supplements are not regulated by any governing agency, like the FDA.  

Other Questions

Is methionine safe for infants or children?

Methionine may be safe for infants and children, but the provider should always be consulted before use. In a study published by the Journal of Nutrition, infants given two to five times the normal amount of methionine did show signs of impaired growth, but no long-term adverse effects were noted.

Which food sources are highest in methionine?

All foods contain some methionine, but according to the journal Nutrition and Metabolism, those containing the highest amount include fish, meat, and eggs.

Do vegetarians need to take methionine supplements to get enough sulfur in the diet?

Interestingly, research has shown that some vegetarians have higher blood concentrations of methionine than in those who are meat-eaters, therefore all vegetarians do not necessarily need to take methionine supplements.

A Word From Verywell

When it comes to many natural supplements, such as methionine, there is a lack of clinical research data to definitively prove safety and efficacy, particularly in human studies. This does not mean that the supplements are not effective, it is an indication, rather, that consultation with a medical professional is imperative to ensure safe and effective use of the supplement. Methionine is a unique nutrient, in that some benefits are from increasing methionine in the diet, and other benefits come from a diet low in methionine. As with all natural and herbal supplements, always consult with a professional healthcare provider before taking methionine.


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9 Sources
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