Serious L-methionine side effects have been reported when using high doses of this supplement. While the human body needs this amino acid in order to function properly, using too much can be dangerous to your health.
Methionine is naturally found in many common foods, including fish, beans, nuts meats and dairy products. When dietary intake is not believed to be sufficient, some people may take methionine supplements to raise levels of this amino acid.
Bodybuilders and athletes commonly use L-methionine supplements to support protein synthesis and lean muscle mass growth. In addition to remedying dietary deficiencies, the Natural Medicines Database reports that this supplement has been studied for a number of medicinal uses.
The Natural Medicines Database also reports that this supplement is considered possibly safe when it is used appropriately, but methionine side effects may still occur. Adverse reactions may be linked to Methionine overdose.



- Used to make the anti-oxidant glutathione
- Supports detoxification pathways
- Can be converted into SAMe
Signs of Methionine Deficiency
L-methionine plays a role in a number of different mechanisms, including protein building, tissue repair, protection from pollutants and detoxification.
Without the appropriate amount of this amino acid, individuals may experience symptoms of deficiency. However, because the body cannot produce methionine on its own, individuals must acquire their entire supply of this amino acid from external sources.
Some people with methionine deficiency may not show any symptoms. However, others may exhibit problems with muscle strength and coordination, skin integrity and detoxification of the liver. The severity of these symptoms may vary based on the severity of the deficiency.
Methionine Uses
The Natural Medicines Database reports that methionine supplementation has been used for the following purposes in addition to the treatment of methionine deficiency.
- Schizophrenia
- Allergies
- Alcoholism
- Depression
- Testing for hyperhomocysteinemia
- Preventing liver damage from acetaminophen poisoning
- Alleviation of radiation side effects
- Copper toxicity
- Asthma
- Parkinson’s disease
- Drug withdrawal
L-Methionine has not been approved by the FDA as a drug to prevent or treat any specific medical condition. More research is needed to understand its medicinal effects and benefits.
Is Methionine Safe?
Methionine safety may depend on the amount of supplement consumed. According to the Natural Medicines Database, methionine supplementation is possibly safe when the supplement is taken in oral or intravenous form and used appropriately.
The supplement is considered possibly safe for both children and adults. However, when methionine supplements are taken in higher doses, they are not considered safe.
Methionine Supplement Side Effects
Some of the possible adverse effects of methionine may include drowsiness, nausea and vomiting. When higher doses of the supplement are consumed, WebMD also reports that the following side effects may occur:
- Increased tumor growth
- Brain damage
- Increased blood levels of homocysteine, which may raise the risk of cardiovascular problems
- Death
If you experience any worrisome side effects while taking methionine supplements, discontinue the supplement and talk to your doctor. If side effects are severe, or if you think you may be having an allergic reaction to methionine supplements, seek immediate medical attention.
Methionine Interactions and Contraindications
At this time, research studies have not found any evidence indicating that methionine supplements interact with prescription medications or other supplements.
Methionine supplements are also considered to be safe when taken with most foods. However, a diet high in nitrite, salt and methionine may increase the risk of certain problems, including gastric cancer.
Methionine may not be safe for people with certain medical conditions. These conditions include:
- Acidosis – Methionine may change the pH of serum, which may be dangerous for people with acidosis.
- Atherosclerosis – Consuming too much methionine may exacerbate atherosclerosis by increasing homocysteine levels.
- Cirrhosis of the Liver or Liver Disease – In people with existing liver damage, methionine supplementation may increase the damage.
- Methylenetetrahydrofolate reductase deficiency – People with MTHFR deficiency may suffer worsened symptoms when taking methionine supplements.
- Schizophrenia – Studies have shown that high doses of methionine in people with schizophrenia may lead to various symptoms, including listlessness, delirium, agitation and confusion.
Methionine supplementation is not recommended for pregnant women or women who are breastfeeding, as it is not known how methionine supplements will affect members of these populations.
How to Take Methionine Safely
Because the negative side effects of methionine may be worsened if used improperly, it is important to use this supplement carefully.
At this time, the United States Food and Drug Administration has not approved methionine supplements for the treatment of any condition. Thus, standardized dosing guidelines are not available for this supplement.
However, the Natural Medicines Database reports that the following dosages have been well tolerated with no serious side effects during past clinical trials.
- Acetaminophen toxicity – 2.5 grams of methionine at four hour intervals within 10 hours of acetaminophen ingestion.
- Parkinson’s disease – 5 grams of methionine daily for two weeks to six months.
- Insomnia – 500 mg of methionine just before bedtime.
The dosages above may not be appropriate for everyone. In order to minimize the risk of methionine side effects as much as possible, begin with a low dosage of methionine and gradually increase the amount you take until you reach the desired level of effectiveness or your doctor’s maximum dosage recommendation.
All people taking methionine should avoid dosages of more than 100 mg per kg of body weight, as dosages of this size may cause severe and potentially fatal cerebral effects.
As with all supplements, you should not begin taking methionine until you have spoken with your doctor about the safety of this supplement. If you experience adverse reactions or negative side effects when taking L-Methionine pills, discontinue use and seek medical attention.
Article last updated on: March 12th, 2018 by Nootriment
1 Comment
Horrible reaction to the amino acid, Methionine. It started with severe muscle cramping and histamine reaction that ended with a sinus and ear infection. Still suffering the after effects of this. In addition, the brain fog and fatigue is making life very hard right now. I will NEVER take this again. It is poison to me.