What Are the Side Effects of Methionine?

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  • Written By: K.C. Bruning
  • Edited By: John Allen
  • Last Modified Date: 21 November 2018
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If used correctly, methionine rarely causes any adverse symptoms. The most common side effects of methionine supplements are nausea, vomiting and drowsiness. It may also worsen the symptoms of liver disease, acidosis, atherosclerosis, and the genetic condition methlyenetetrahydrofolate reductase (MTHFR) deficiency.

In order to avoid the most dangerous side effects of methionine, it is important to consult a medical professional in order to learn the correct dosage for the condition being treated. Though the amino acid is found naturally in foods such as sesame seeds, fish, and cereal grains, it is much more potent in supplement form. The more serious methionine side effects are often the result of a patient taking excessive amounts of the substance.

When taken in large amounts, the resulting side effects of methionine can cause permanent damage to the body, including serious medical conditions or death. By ingesting an excess of the supplement, it is possible to trigger the symptoms of schizophrenia, which include confusion, agitation, and delirium. It can also cause brain damage and potentially encourage the growth of tumors. There is also a possibility that taking too much of the supplement can raise the levels of homocysteine in the blood, which has been linked to heart disease.


An allergic reaction is one of the other serious side effects of methionine. This includes swelling in the areas from the neck up, chest tightness, rash, hives, and breathing problems. Emergency medical attention should be sought if any of these symptoms appear as a result of taking the supplement.

There are some conditions which may make taking methionine too risky or at least require a special dosage or increased doctor observation. Pregnant or nursing women are usually advised not to take the drug. It may also be problematic for patients with liver conditions or elevated levels of stomach acid. Patients with serious liver problems are typically advised not to take the supplement.

In general, methionine is used to add acid to urine by neutralizing its ammonia content. The drug is often used to treat patients who have ingested too much acetaminophen. When administered intravenously within approximately ten hours of the poisoning, it can prevent death from an overdose.

The supplement has also been used with animals. It has grown in popularity as an organic poultry feed supplement. The supplement has been added to some commercial pet foods as well. Methionine is also an ingredient in a product that lowers dog urine pH so that it does not harm grass.


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Post 5

What about the methionine in s-adenosylmethionine, please. Are there mitigating effects on methionine overproduction due to the s-adenosyl?

Post 4

This is totally weird. They want us buying drugs, not supplements. I have advanced chronic fatty liver/liver failure and I'm on methionine and I'm feeling so much better since I started it. I take it with lecithin and I've lost a lot of weight without exercise. I take one 500mg cap twice a day. I have mo side effects whatsoever and I do have acidosis; as I've found out from testing many times prior via urine strips. I have candida and parasites which cause acidosis.

I feel a lot better on methionine which takes care of the excess ammonia to the brain, which can be truly lethal. I'm off to research this homocysteine business.

Post 3

I've just started taking l-methionine as well and I'm not worried about common side effects like insomnia or dizziness. But I read on the product description that it can also cause side effects like aggression or suicidal thoughts in the long term. These are the kind of side effects that scare me the most because I think that if you're experiencing mental and emotional side-effects, it might be harder to realize it.

I guess l-methionine should be treated like medication. I have taken anxiety and depression medications before and suicidal thoughts and aggression was listed as a side effect in those as well. L-methionine is natural but this definitely doesn't mean that it's harmless.

I'm taking 300mg daily

right now. Do you think this is a high dose? Should I worry about some of the long-term side effects?

What the safest dose that can be taken which will still benefit me with the least side effects?

I would love to hear from other people who are taking this.

Post 2

@burcidi-- I'm not an expert on this subject and I can't tell you the details of how it works. But I know that SAM-e stands for "s-adenosyl-l-methionine."

From what I understand it's not methionine per se , but it is supposed to naturally transform into methionine in the body. So we could say that it is a methionine supplement. I don't even think that it is available in any other form commercially.

Compared to the side effects mentioned in the article, the side effects you mentioned do seem very minor. I think digestive issues are common side effects. I've heard of it causing nausea, bloating, diarrhea or constipation before as well.

Post 1

I'm taking SAM-e supplement for depression. I think this is the same as methionine, or methionine is the main ingredient. It was recommended to me by my doctor, he said many people benefit from using it and it's completely natural.

I've been using it for over a month and I do see an improvement in my mood. But I'm also seeing a lot of side effects so I don't know how long I will continue to use it.

The side effects I've noticed so far are gas, difficulty sleeping and dry mouth. I think these are not very bad, many people would consider this very normal and acceptable. It is a little bothersome though. I wish I could benefit from methionine without the side effects.

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