What Are the Risks of Taking Glycine?

November 1, 2025 •

4 min read

While glycine is a naturally occurring amino acid generally considered safe, some reports indicate mild side effects in some individuals. Understanding what are the risks of taking glycine is crucial before starting a supplementation regimen to ensure safety.

Quick Summary

Glycine supplementation is generally safe in moderate doses, but can cause mild gastrointestinal issues, drowsiness, and interact with certain medications. Higher doses or existing health conditions warrant medical supervision.

Key Points

Moderate Doses Are Generally Safe: For most healthy adults, taking glycine in moderate doses of 1-5 grams per day is well-tolerated and side effects are uncommon.
High Doses Increase Risk: Exceeding 10-15 grams per day or using medically administered, high-concentration glycine poses a higher risk for more severe side effects, including neurological and cardiac issues.
Gastrointestinal Side Effects Are Possible: Mild side effects such as nausea, upset stomach, or diarrhea have been reported in some individuals, particularly at higher dosages.
Interactions with Medications Occur: Glycine can interact with antipsychotics (like clozapine), sedatives, and blood pressure medications, potentially reducing their effectiveness or amplifying their effects.
Exercise Caution with Health Conditions: Individuals with liver disease, kidney disease, or a history of stroke should use glycine only under medical supervision.
Avoid If Pregnant or Breastfeeding: Due to a lack of safety data, pregnant and breastfeeding women are advised to avoid glycine supplements.

Understanding the Safety Profile of Glycine

Glycine is the simplest amino acid and plays a vital role in many physiological functions, from protein synthesis to acting as a neurotransmitter. While it is naturally produced by the body and found in many foods, supplemental glycine is commonly used for improving sleep, supporting muscle health, and other purported benefits. For most healthy individuals, moderate doses of glycine are well-tolerated. However, like any supplement, it is not without potential risks, especially at higher doses or for certain individuals with pre-existing health conditions or who are taking other medications.

Common and Mild Side Effects

Though many people experience no adverse effects, some users have reported mild and temporary side effects, particularly when first starting supplementation or taking higher doses. These symptoms typically resolve after the supplement is discontinued or the dosage is lowered.

Gastrointestinal Distress

Nausea and Vomiting: A few people have experienced these symptoms, though they are considered rare.
Stomach Upset and Diarrhea: General stomach discomfort, soft stools, or diarrhea have also been reported, especially with higher dosages.

Neurological Effects

Drowsiness: Because glycine acts as an inhibitory neurotransmitter, it can cause feelings of sleepiness or excessive sedation in some individuals. This is often the desired effect when used for sleep, but can be a risk if it impairs daytime function. Some report a feeling of dullness.

Serious Risks and Contraindications

For certain groups, the risks of taking glycine are more significant and require a consultation with a healthcare professional.

Drug Interactions

Glycine can interact with several types of medications, and combining them can either reduce the medication's effectiveness or increase side effects.

Antipsychotics (e.g., Clozapine): Glycine may decrease the effectiveness of antipsychotic medications used for schizophrenia. Individuals taking Clozapine should not take glycine supplements.
Sedatives: Glycine's calming properties can enhance the effects of other sedatives.
Blood Pressure Medications: Glycine may lower blood pressure, which could enhance the effects of antihypertensive drugs and cause an unsafe drop in blood pressure.

Specific Health Conditions

Kidney and Liver Disease: The metabolism and excretion of glycine involve the kidneys and liver. For individuals with existing disease in these organs, glycine supplementation could pose a risk, and it is best avoided.
Pregnancy and Breastfeeding: There is insufficient reliable information on the safety of glycine for pregnant and breastfeeding women, so it is recommended to avoid use.
Children and Infants: The safety of glycine for young children has not been fully studied. Infants with nonketotic hyperglycinemia (NKH) cannot properly metabolize glycine, leading to severe neurological symptoms. In general, single amino acid supplements for children are not advised without medical supervision.
Stroke: Glycine should not be taken by people who have had a stroke unless supervised by a doctor.
Allergies: Though rare, allergic reactions like rash, itching, or difficulty breathing can occur.

Risks of High and Chronic Glycine Doses

While doses up to 30 grams per day have been used in some studies for specific conditions under medical supervision, long-term, high-dose usage has not been extensively researched. Risks associated with high intake levels include:

Visual Disturbances: High doses, particularly when administered medically as an irrigant during surgery, can cause blurred vision or transient blindness.
Hyperammonaemia: Very high glycine doses can lead to elevated blood ammonia, potentially causing depressed consciousness in some individuals.
Cardiac Toxicity: In animal studies, high concentrations of glycine have shown potential to damage heart tissue, a risk not yet fully evaluated in humans.
Nitrogen Imbalance: Long-term high doses of single amino acids, including glycine, can cause a negative nitrogen balance, straining kidney function and negatively impacting the metabolism of other amino acids.

Comparison of Low vs. High Glycine Dosage Risks


Risk Type	Low Dosage (e.g., 1–5 grams/day)	High Dosage (e.g., >10-15 grams/day or medically administered)
Common Side Effects	Mild stomach upset, nausea, or drowsiness reported rarely.	Higher risk of gastrointestinal issues, increased drowsiness.
Serious Complications	Extremely rare; generally considered safe for most healthy adults.	Potential for visual disturbances, hyperammonaemia, cardiac issues, and nitrogen imbalance.
Drug Interactions	May still interact with medications like antipsychotics, sedatives, or blood pressure drugs, even at lower doses.	More pronounced risk of intensifying sedative effects or interfering with other medications.
Long-Term Effects	Limited long-term human data, but generally considered safe.	Safety of chronic high-dose use is not well-studied; long-term effects are largely unknown.

Conclusion: Prioritizing Safety with Glycine Supplementation

While glycine is an amino acid with many potential health benefits, it is crucial to approach supplementation with caution and a healthy dose of skepticism. The majority of risks associated with glycine are linked to excessively high doses or specific pre-existing health conditions. For most healthy adults taking moderate doses (typically 1-5 grams per day), side effects are usually mild and uncommon. However, those on specific medications or with liver, kidney, or neurological issues should consult a doctor before beginning any glycine regimen. Always remember that a supplement is not a substitute for a balanced diet and a healthy lifestyle. Adhering to recommended dosages and seeking professional medical advice can help ensure you can experience any potential benefits while mitigating the risks associated with taking glycine.

Learn more about glycine and other amino acids from authoritative medical resources such as the National Institutes of Health (NIH).

Frequently Asked Questions

The most commonly reported side effects of glycine, especially with higher dosages, include mild gastrointestinal issues like stomach upset, nausea, vomiting, or diarrhea. Some people may also experience drowsiness.

You should consult a healthcare provider before taking glycine if you are on any medication. Glycine can interact with certain drugs, such as antipsychotics (especially clozapine), sedatives, and blood pressure medication.

While moderate doses appear safe for short-term use, extensive research on the long-term effects of high-dose glycine supplementation in humans is limited. High doses over time could potentially cause nitrogen imbalance.

Taking excessively high doses of glycine, especially in acute medical settings, can lead to signs of toxicity including visual disturbances, drowsiness, vomiting, weakness, and skin flushing. Chronic high-dose use is not well-studied.

Pregnant or nursing women, children, and individuals with pre-existing liver or kidney disease should avoid glycine unless advised by a doctor. People taking clozapine or with a history of stroke should also use caution.

Glycine is metabolized and processed by the liver and kidneys. Individuals with impaired function of these organs may be at a higher risk of complications from glycine supplementation, which can stress these systems.

Although rare, allergic reactions to glycine are possible. Symptoms can range from a mild rash or itching to severe anaphylaxis in sensitive individuals. Stop taking the supplement and seek medical help if an allergic reaction occurs.