Who Should Not Take Glycine? A Guide to Precautions and Contraindications

November 27, 2025 •

4 min read

While glycine is a naturally occurring amino acid generally considered safe, some individuals must exercise extreme caution or avoid supplementation entirely due to pre-existing conditions or medication use. Understanding who should not take glycine is critical to preventing adverse effects and ensuring optimal health outcomes.

Quick Summary

This article outlines the key populations who should avoid or be cautious with glycine supplementation, including those with certain medical conditions, women who are pregnant or nursing, and individuals on specific medications. Safety and contraindications are detailed.

Key Points

Pregnant or Nursing Women: Avoid glycine supplements due to a lack of safety data during pregnancy and breastfeeding.
Liver or Kidney Disease: Individuals with impaired liver or kidney function should avoid glycine as it can worsen their condition.
Antipsychotic Medication Users: Do not take glycine if you are on clozapine, as it may decrease the drug's effectiveness.
On Sedatives or Blood Pressure Medication: Caution is advised as glycine can increase drowsiness or lower blood pressure, interacting with these medications.
History of Glycine Allergy: Anyone with a known allergic reaction to glycine should avoid supplementation entirely.
Children: Glycine supplements are not recommended for children without medical supervision due to insufficient research.

Precautions and Risks of Glycine Supplementation

Glycine is a non-essential amino acid known for its potential benefits related to sleep, collagen production, and antioxidant support. However, as with any supplement, it is not universally safe for everyone. The decision to take glycine should be made with careful consideration of one’s overall health, existing medical conditions, and current medication regimen, ideally in consultation with a healthcare professional.

Individuals with Kidney or Liver Disease

For individuals with pre-existing kidney or liver conditions, glycine supplementation poses a significant risk. The body's ability to process and eliminate amino acids can be impaired by these diseases. Accumulation of amino acids, including glycine, could worsen the underlying condition or lead to a nitrogen imbalance. While some animal studies suggest glycine can protect the liver from certain types of damage, this protective effect has not been confirmed in human patients with severe disease, and supplementation should not be attempted without strict medical supervision.

Kidney Disease: Impaired kidney function can cause amino acids to build up to harmful levels in the body.
Liver Disease: Individuals with severe liver conditions, especially alcohol-induced liver damage, should consult a doctor before use, as the liver’s ability to metabolize supplements is compromised.
Anuria: People with anuria, a condition of no urine output, must avoid glycine due to the inability to excrete waste products effectively.

Pregnancy and Breastfeeding

Due to insufficient safety data, pregnant and breastfeeding women are advised to avoid glycine supplements unless explicitly recommended and supervised by a healthcare provider. While some research suggests a potential need for glycine during late pregnancy, especially if dietary protein is low, supplementation should only occur under medical guidance. The safety for the developing fetus and nursing infant has not been definitively established.

Children and Infants

Children should not be given glycine supplements without medical authorization. The appropriate dosage and long-term effects on a child's developing body are not well understood, making it a precaution for this vulnerable population.

Drug Interactions with Glycine

Glycine's role as a neurotransmitter means it can interact with medications that affect the central nervous system. These interactions can alter the effectiveness of the drug or increase side effects.

Antipsychotics: Glycine can reduce the effectiveness of antipsychotic medications, notably clozapine, which is used to treat schizophrenia. Combining them can interfere with the drug’s intended effect.
Sedatives and Muscle Relaxants: Since glycine has a calming effect, taking it with sedatives, anti-anxiety medications (like benzodiazepines), or muscle relaxants may increase drowsiness and fatigue to dangerous levels.
Antihypertensive Drugs: Glycine may have a blood-pressure-lowering effect, which can enhance the effects of blood pressure medication. Close monitoring is necessary to prevent blood pressure from dropping too low.
Antidepressants and Antiepileptics: It may interact with certain antidepressants (e.g., fluoxetine) and antiepileptics (e.g., valproic acid), altering their efficacy or increasing side effect risks.

Individuals with Allergies to Glycine

Though uncommon, a known allergy or unusual reaction to glycine is a direct contraindication. Symptoms of an allergic reaction can include a rash, itching, or difficulty breathing.

Comparison of Glycine Benefits vs. Risks


Feature	Generally Considered Safe (with precautions)	Potential Risks (for specific groups)
Population	Healthy adults in appropriate doses.	Pregnant or nursing women, children, individuals with liver or kidney disease.
Dosage	3-6 grams daily is commonly used in studies.	High doses can cause nausea, vomiting, or sedation.
Context	Short-term use for sleep or other non-therapeutic purposes.	Use alongside specific medications like clozapine, sedatives, or blood pressure drugs.
Health Status	Good overall health.	Pre-existing conditions like liver disease, kidney failure, or specific neurological issues.

Potential Side Effects for Anyone

Even among those without contraindications, high doses of glycine can lead to mild side effects. It's important to monitor your body's response, especially when starting a new supplement regimen.

Nausea and vomiting
Stomach upset and diarrhea
Excessive drowsiness or dullness, particularly at high doses
In rare cases, allergic reactions

Conclusion: Prioritize Medical Consultation

While a powerful and useful amino acid for many people, glycine is not a one-size-fits-all supplement. The phrase "who should not take glycine" points to specific populations and circumstances where the risks may outweigh the potential benefits. This includes individuals with pre-existing conditions affecting the liver or kidneys, pregnant or breastfeeding women, children, and people taking medications for psychiatric, neurological, or cardiovascular issues. Always consult a healthcare provider before starting any new supplement, especially if you have an underlying health condition or are on other medications, to ensure it is a safe and appropriate choice for your individual health goals. For more in-depth information, the National Institutes of Health provides robust resources on supplement safety.

Frequently Asked Questions

Yes, individuals with pre-existing liver disease, particularly severe cases, should not take glycine supplements without consulting a healthcare professional. An impaired liver may not metabolize amino acids correctly, which can exacerbate the condition.

Yes, glycine can interact with certain psychiatric medications. It is known to interfere with the effectiveness of the antipsychotic drug clozapine, and it can increase sedation when taken with other sedatives.

The primary reason is the lack of reliable and conclusive safety data regarding glycine's effects during pregnancy and breastfeeding. It is considered a precaution to avoid its use unless under the direct supervision of a doctor.

Glycine has the potential to lower blood pressure. When taken with antihypertensive drugs, this effect could be amplified, leading to blood pressure dropping to dangerously low levels. Blood pressure should be closely monitored in this case.

No, glycine supplements are generally not recommended for children. There is not enough research to establish safe dosages or long-term effects on a child's development, so it is best to avoid it.

If you have a known allergy to glycine or its components, you must avoid it. An allergic reaction could manifest as a rash, itching, or breathing difficulties, and you should stop taking it and contact a doctor immediately.

For those who do not have a specific contraindication but take high doses, some mild side effects can occur, including stomach upset, nausea, vomiting, diarrhea, or excessive drowsiness.