What are the symptoms of too much magnesium Threonate?

November 24, 2025 •

3 min read

While magnesium is a vital mineral for over 300 bodily processes, excessive intake from supplements can lead to a condition known as hypermagnesemia, which has its own set of risks. Understanding what are the symptoms of too much magnesium threonate is critical for anyone considering supplementation, especially given its popularity for cognitive support.

Quick Summary

Overconsumption of magnesium threonate can cause a range of symptoms, including mild gastrointestinal issues like nausea and diarrhea, as well as more severe signs such as low blood pressure, muscle weakness, confusion, and irregular heartbeat. Individuals with impaired kidney function face a higher risk of magnesium toxicity, as their bodies cannot efficiently clear the excess mineral.

Key Points

Mild Symptoms: Common, less serious side effects of too much magnesium threonate include nausea, diarrhea, headaches, flushing, and drowsiness.
Severe Toxicity (Hypermagnesemia): In rare, severe cases, excessive intake can lead to low blood pressure, muscle weakness, confusion, and irregular heartbeat.
Higher Risk Groups: Individuals with pre-existing kidney problems are at the highest risk for magnesium toxicity because their bodies cannot efficiently remove excess magnesium.
Dosage Matters: While considered gentle on the stomach, excessive doses of magnesium threonate, as with any form, increase the risk of side effects.
When to Get Help: Seek immediate medical attention if severe symptoms such as irregular heartbeat, difficulty breathing, or severe drowsiness occur.
Comparative Side Effects: Magnesium threonate generally has fewer gastrointestinal side effects than forms like magnesium oxide but shares the same risks of hypermagnesemia if overused.

Understanding Magnesium Threonate

Magnesium L-threonate is a newer form of magnesium gaining popularity, primarily for its ability to cross the blood-brain barrier and enhance magnesium levels in the brain. This is thought to improve cognitive function, memory, and support overall brain health. As with any supplement, while it offers benefits, it is crucial to understand the risks associated with taking too much. The kidneys are responsible for flushing out excess magnesium, but problems arise when intake is excessive or kidney function is impaired.

Common Symptoms of Excess Magnesium Threonate

Exceeding the recommended dosage of magnesium threonate can lead to an accumulation of magnesium in the blood, causing common side effects. While magnesium threonate is generally well-tolerated and less likely to cause digestive upset than other forms like oxide or citrate, high doses can still lead to problems.

Mild Gastrointestinal Distress: Nausea, stomach cramps, and diarrhea are among the most frequently reported side effects of too much supplemental magnesium. This occurs because excess magnesium can have a laxative effect.
Headaches and Drowsiness: Some individuals may experience headaches or a sedative effect, feeling drowsy or fatigued. This is a milder symptom that may subside as the body adjusts to the supplement or with a dosage reduction.
Flushing: A sensation of warmth and redness, particularly in the face, can also occur.

Severe Signs of Magnesium Toxicity

In rare cases, particularly with very high doses or in individuals with pre-existing conditions like kidney disease, excessive magnesium can lead to a severe and potentially life-threatening condition called hypermagnesemia.

Neuromuscular Issues: Muscle weakness, lethargy, and a decrease or loss of deep tendon reflexes can occur as magnesium levels rise significantly.
Cardiovascular Complications: Serious cardiovascular problems can develop, including hypotension (low blood pressure) and irregular heartbeat (cardiac arrhythmia). In extreme cases, hypermagnesemia can lead to cardiac arrest.
Respiratory Depression: High levels of magnesium can depress the central nervous system, leading to slowed or difficult breathing.
Mental and Neurological Changes: Confusion, severe drowsiness, and impaired neurological function are possible.

Comparison of Magnesium Forms and Side Effects

Not all magnesium supplements are equal in their side effect profiles. The form of magnesium impacts its absorption rate and potential for gastrointestinal side effects. For example, magnesium oxide is known for its high risk of a laxative effect, while magnesium glycinate is often cited as being much gentler on the digestive system.


Feature	Magnesium Threonate	Magnesium Glycinate	Magnesium Oxide
Primary Use	Cognitive health, brain support	Relaxation, sleep, stress reduction	Constipation relief, general supplementation
Absorption	High, crosses blood-brain barrier	High, gentle on the stomach	Poor
Gastrointestinal Side Effects	Generally low risk, mild discomforts possible	Very low risk, considered gentle	High risk of diarrhea and GI upset
Cognitive Effects	Designed to increase brain magnesium	Calming effects, no specific cognitive-enhancing properties	No specific cognitive effects
Risk of Hypermagnesemia	Low for healthy individuals at recommended doses, higher with pre-existing kidney issues	Low for healthy individuals at recommended doses	High with large doses, especially with impaired renal function

Who is at Higher Risk?

While hypermagnesemia from oral supplementation is rare in healthy individuals, certain groups are at a higher risk. Individuals with impaired renal function or chronic kidney disease are particularly vulnerable because their kidneys are less efficient at filtering out excess magnesium. Other risk factors can include:

Elderly individuals
Those with certain gastrointestinal diseases
People taking large doses of magnesium-containing medications, such as laxatives or antacids.

When to Seek Medical Attention

It is crucial to stop taking the supplement and contact a healthcare provider immediately if you experience severe symptoms like irregular heartbeats, severe low blood pressure, muscle weakness, confusion, or difficulty breathing. In cases of severe overdose, seek emergency medical care by calling emergency services or a poison control center.

Conclusion

Magnesium threonate offers targeted cognitive benefits but is not exempt from the risks of excessive magnesium intake. While mild side effects like diarrhea and nausea are the most common signs of overdoing it, severe magnesium toxicity, or hypermagnesemia, can pose serious health risks, especially for those with compromised kidney function. It is always best to adhere to the recommended dosage, be aware of potential symptoms, and consult with a healthcare professional before starting or adjusting any supplement regimen. Awareness and moderation are key to enjoying the benefits of magnesium threonate safely.

For more detailed information on magnesium toxicity, please refer to the National Institutes of Health (NIH) Office of Dietary Supplements fact sheet on magnesium, a recognized authority on nutritional information.(https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/)

Frequently Asked Questions

It is extremely rare to get too much magnesium from food sources alone, as the kidneys are highly effective at filtering out dietary excess. Magnesium toxicity is nearly always associated with supplement overuse.

For adults, the tolerable upper intake level (UL) for supplemental magnesium is generally 350 mg per day. It is important to note this limit applies to supplements only, not dietary intake.

Yes. Certain forms of magnesium, such as magnesium oxide and citrate, are more likely to cause gastrointestinal issues like diarrhea compared to magnesium threonate and glycinate, which are considered gentler on the digestive system.

Symptoms of excess magnesium range from mild digestive upset to more serious issues like low blood pressure or muscle weakness. If you recently started or increased a magnesium supplement and experience these symptoms, it could be a sign of overconsumption.

If you suspect you have taken too much and are experiencing severe symptoms, stop taking the supplement and seek medical help immediately. For mild symptoms, discontinuing the supplement often resolves the issue.

Yes, some individuals may experience drowsiness or a sedative effect when taking magnesium threonate, especially when they first start. This is why some people prefer taking it in the evening.

Hypermagnesemia is the medical term for having an excessively high level of magnesium in the blood. It is a rare but serious condition, most commonly seen in people with impaired kidney function who are taking high-dose magnesium supplements.