L-Methionine: Benefits, Risks, and Sources

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

L-methionine is an essential amino acid needed for many body functions, including building new proteins, supporting DNA activity, and repairing tissues. It also has a vital role in helping cells neutralize free radicals, toxins that damage tissues and lead to conditions like cancer.

Your body can’t produce L-methionine, so you must get it from your diet or supplements. People often take them to treat various health conditions, but more research is needed to support these uses. In some cases, L-methionine supplements may cause as much harm as good since taking too much of it is associated with side effects.

In the United States, the Food and Drug Administration (FDA) does not regulate supplements the way it regulates prescription drugs. That means some supplement products may not contain what the label says. When choosing a supplement, look for third-party tested products and consult a healthcare provider, registered dietitian nutritionist (RD or RDN), or pharmacist.

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L-methionine is considered an essential amino acid because it must be consumed from the diet. Our bodies cannot produce it.

L-methionine may be beneficial for various health conditions. However, many of these are not well-supported by scientific evidence. Below is a look at some of the better-supported uses of L-methionine.

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian nutritionist (RD or RDN), pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

One of the leading uses of L-methionine is in the treatment of an acetaminophen overdose.

Acetaminophen, or Tylenol, is a common, over-the-counter (OTC) pain reliever. If a person takes too much acetaminophen, then swift action is needed to prevent liver damage or even possible death.

Oral L-methionine taken within 10 hours has been used to treat acetaminophen overdose. L-methionine is thought to prevent the byproducts of acetaminophen from damaging the liver as a result of an acetaminophen overdose.

However, it should be pointed out that there are other treatment options and that L-methionine may not be the most effective one for an acetaminophen overdose.

L-methionine has been studied for its role in cancer risk. However, the results are conflicting.

Some studies show that L-methionine may be helpful for breast and pancreatic because it can interrupt the cell growth cycle, leading to cell death. In lab studies, it has been shown to be effective in liver cancer cells as well.

However, these findings have not always been replicated in studies examining the relationship between L-methionine and cancer. In fact, some studies have shown that L-methionine restriction may lead to a lower risk of cancer.

A review from 2020 noted that L-methionine is an integral part of the growth cycle in certain types of cancer cells. According to the review, evidence that L-methionine restriction may inhibit cancer cell growth is growing.

More human trials are needed to confirm whether L-methionine supplementation or L-methionine restriction would be beneficial for cancer risk reduction. Until then, L-methionine should not be used for this purpose.

Neural tube birth defects are some of the most common birth defects, and L-methionine may help in preventing them.

The neural tube develops in the third and fourth weeks of pregnancy. It eventually forms the baby's brain, skull, spinal cord, and backbones. Neural tube defects result from the tube not closing properly. Examples include spina bifida, anencephaly, and encephalocele.

Although more research is still needed in this area, some evidence suggests that L-methionine may be able to help prevent these types of birth defects. In a small study, the participants who had a higher intake of L-methionine in their diet were less likely to have babies born with neural tube defects.

L-methionine may help improve liver damage, especially when used alongside other treatments.

A 2020 review found that L-methionine supplementation may help reduce the risk of liver damage. Supplementing with L-methionine may help increase levels of S-adenosyl methionine (SAMe), which may protect against liver damage.

However, these findings may be controversial, and L-methionine may not be right for people with severe liver disease. Again, stronger research is needed to support these claims.

L-methionine is thought to have other potential benefits, including:

However, like many of the potential uses of L-methionine, the research supporting these health claims is limited.

Many foods contain L-methionine, making it easy to get all you need from your diet.

L-methionine is found in the greatest amounts in animal foods. It is present in plant-based foods in smaller amounts.

Food sources of L-methionine include:

Many of these foods are proteins, which makes sense because L-methionine is used to make proteins. Typically, a well-balanced diet containing various fruits, vegetables, grains, healthy fats, and lean protein will provide you with all the L-methionine and other nutrients your body needs.

Since L-methionine is found in plenty of plant-based foods, vegetarians do not necessarily need to take L-methionine supplements to get enough sulfur.

L-methionine supplements are available in capsule form. You may also find supplements that contain L-methionine and other nutrients, like various amino acids. These also tend to be sold as capsules.

Vegan versions of L-methionine supplements are available. If you are vegan or vegetarian, choose a plant-based L-methionine supplement.

It is best to select an L-methionine supplement that has been certified by a third party, like U.S. Pharmacopeia, NSF International, or Consumer Lab. Since the FDA does not closely regulate supplements like drugs, those certified are more likely to contain the ingredients they say they do.

Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage is appropriate for your individual needs.

There is no standard dose for L-methionine supplements. However, there is a recommended daily intake of L-methionine from food and other sources.

In healthy adults, the current recommended dose for sulfur amino acids, whether L-methionine or cysteine (another sulfur-containing amino acid) is 15 milligrams per kilogram of body weight per day.

Using this math, a 150-pound person would need about 1 gram of L-methionine (or cysteine) per day. This gives you all the sulfur your body needs to build important proteins.

The right dosage for you may depend on several factors, such as your current health, age, and sex. Talk with your healthcare provider about using L-methionine safely before you start taking supplements.

Improper storage of L-methionine supplements can cause spoiling. L-methionine should be stored in a cool, dry place that is not in direct sunlight. It is best to keep L-methionine supplements in the air-tight container they came in.

L-methionine supplements should be discarded once they reach the expiration date listed on the packaging.

Due to the possibility of overdose, keep L-methionine supplements out of reach of pets and small children.

Side effects are always possible when taking supplements, and L-methionine is no exception. L-methionine side effects can be mild or severe.

L-methionine is thought to be safe for most people to take at normal doses.

Common side effects associated with L-methionine tend to be mild and include:

The best way to avoid side effects as much as possible is to take L-methionine supplements as directed. Oftentimes, side effects are more likely when supplements are taken incorrectly or if the dose is too high.

High blood homocysteine can lead to heart disease and other complications. To lower your risk of heart disease while taking L-methionine supplements, make sure you're getting enough folic acid, vitamin B-6, and vitamin B-12. This helps prevent high levels of homocysteine in the blood.

In general, L-methionine is thought to be safe. However, severe side effects are possible if it is taken incorrectly. These may include high cholesterol levels, which increases the risk of cardiovascular disease, heart attack, and stroke.

Although extremely rare, it is possible to overdose on L-methionine. L-methionine toxicity or an overdose can happen over time with a build-up of L-methionine or after one large dose of L-methionine.

In addition, high levels of L-methionine have been associated with an increased risk of diabetes. In a study of Chinese adults, a diet high in L-methionine was linked with diabetes, regardless of whether L-methionine came from plant-based or animal-based sources.

Taking too much L-methionine can cause homocysteine levels to rise (hyperhomocysteinemia). Homocysteine is a potentially dangerous compound. It is a known risk factor for cardiovascular disease.

Too much L-methionine has been linked to not only hyperhomocysteinemia but also oxidative stress. Together, these two factors may speed up the aging process, leading to memory problems and cognitive deficits. This increases the risk of neurodegenerative diseases like Parkinson's and Alzheimer's.

L-methionine may not be safe for everyone. Certain populations should avoid using L-methionine or discuss it with their healthcare provider before taking it:

It has also been suggested that L-methionine could make schizophrenia worse for some people. However, the research looking into this claim is not strong. One animal study correlated L-methionine use to behavioral responses and symptoms similar to schizophrenia. It is unknown if these results translate to humans.

To better understand these and other precautions, talk with your healthcare provider about whether L-methionine is safe for you.

L-methionine may be safe for infants and children, but consult your child's healthcare provider about using supplements. Single amino acid supplements like L-methionine can lead to growth problems in children.

L-methionine is an essential amino acid, which means we must consume it. It is found in animal and plant sources. It is one of just two amino acids that contain sulfur and may be helpful for some health concerns. However, research that backs up most of these health claims is lacking.

There are few side effects associated with taking L-methionine, but it is important to take precautions when using it, as an overdose is possible.

L-methionine supplements are not suitable for everyone, so talk with your healthcare provider for additional information before starting L-methionine supplements.

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By Brittany Lubeck, MS, RDNLubeck is a registered dietitian and freelance nutrition writer with a master's degree in clinical nutrition.