What are the side effects of magnesium supplements?

January 9, 2026 •

3 min read

Over 48% of Americans do not get enough magnesium from their diets, leading many to consider supplements. While this mineral is essential for over 300 biochemical reactions in the body, it is crucial to understand what are the side effects of magnesium supplements before starting a new regimen.

Quick Summary

Magnesium supplements, particularly in high doses or with certain forms like oxide and citrate, frequently cause digestive issues such as diarrhea, nausea, and cramping. Excessive intake can lead to hypermagnesemia, a serious condition characterized by muscle weakness, low blood pressure, and irregular heart rhythms.

Key Points

Digestive Discomfort: Common side effects include diarrhea, nausea, and abdominal cramps, especially with high doses or poorly absorbed forms like citrate and oxide.
Magnesium Toxicity (Hypermagnesemia): Excessive intake can lead to serious, though rare, symptoms like muscle weakness, low blood pressure, and irregular heartbeats.
Form Matters: Bioavailability varies among magnesium types; glycinate is typically gentler on the stomach than oxide or citrate.
Kidney Risk: Individuals with impaired kidney function are at significantly higher risk for magnesium toxicity because their bodies cannot excrete the excess mineral.
Drug Interactions: Magnesium can interfere with the absorption and effectiveness of certain medications, including some antibiotics and blood pressure drugs.
Manage Symptoms: To minimize side effects, try starting with a lower dose, taking the supplement with food, or switching to a more easily tolerated form.

Common Digestive Side Effects

Diarrhea and Abdominal Cramping

One of the most frequently reported side effects of magnesium supplements is gastrointestinal distress. This is because unabsorbed magnesium in the intestines creates an osmotic gradient, drawing water into the bowel and leading to a laxative effect. This issue is particularly prevalent with poorly absorbed forms like magnesium oxide, magnesium citrate, and magnesium sulfate, which are sometimes used specifically for their laxative properties.

Magnesium Oxide: Known for its low bioavailability, magnesium oxide is more likely to cause loose stools or diarrhea.
Magnesium Citrate: This form is a common saline laxative, actively pulling water into the intestines to stimulate bowel movements.
High Dosage: The risk of digestive upset increases significantly with higher doses, often above the 350 mg supplemental upper limit for adults.

Nausea and Vomiting

Beyond diarrhea, some individuals experience nausea and vomiting after taking magnesium supplements. This can be a sign that the body is not tolerating the dose or the form of magnesium well. Taking the supplement with food may help mitigate this discomfort.

Serious Side Effects and Magnesium Toxicity (Hypermagnesemia)

While rare in healthy individuals with normal kidney function, magnesium toxicity, or hypermagnesemia, can occur from excessive supplemental intake. The kidneys are typically efficient at flushing out excess magnesium, but this is compromised in people with impaired renal function.

Symptoms of Hypermagnesemia

Early symptoms can be mild and easily confused with less serious issues, but can escalate quickly. Serious symptoms require immediate medical attention.

Initial symptoms: Nausea, diarrhea, abdominal cramping, and fatigue.
More severe symptoms: Muscle weakness, low blood pressure (hypotension), facial flushing, lethargy, and drowsiness.
Severe toxicity: In extreme cases, hypermagnesemia can lead to irregular heartbeat (arrhythmias), respiratory depression, and even cardiac arrest.

Comparison of Magnesium Forms and Side Effects


Type of Magnesium	Primary Use	Bioavailability	Side Effect Profile
Magnesium Oxide	Constipation, Heartburn	Low	High risk of gastrointestinal (GI) side effects, especially diarrhea
Magnesium Citrate	Laxative, Constipation	High	Moderate to high risk of GI side effects; designed to promote bowel movements
Magnesium Glycinate	Sleep, Anxiety, Relaxation	High	Low risk of GI side effects; well-tolerated and gentle on the stomach
Magnesium Malate	Energy, Muscle Pain	High	Low risk of GI side effects
Magnesium Chloride	General Supplement, Topical	High	Moderate risk of GI side effects

Who Should Be Cautious with Magnesium Supplements?

Certain individuals should exercise caution or avoid magnesium supplements entirely unless directed by a healthcare professional.

Individuals with Impaired Kidney Function

People with chronic kidney disease or impaired renal function are at the highest risk for magnesium toxicity. Their kidneys cannot effectively excrete excess magnesium, causing it to build up to dangerous levels in the blood.

Individuals on Specific Medications

Magnesium can interact with various medications, reducing their effectiveness or increasing side effects.

Antibiotics: Magnesium can bind to antibiotics like tetracyclines and quinolones, preventing their absorption.
Diuretics: Some diuretics can either increase or decrease magnesium levels.
Bisphosphonates: Magnesium can interfere with the absorption of these osteoporosis medications.
Blood Pressure Medications: Taking magnesium with calcium channel blockers can cause dangerously low blood pressure.

How to Minimize and Manage Side Effects

If you experience mild side effects, several strategies can help.

Reduce your dosage: Starting with a lower dose and slowly increasing can help your body adjust.
Take with food: Consuming magnesium with a meal can help reduce the risk of gastrointestinal upset.
Split doses: Dividing your total daily dose into smaller portions throughout the day can minimize digestive discomfort.
Change the form: If you experience diarrhea, consider switching from a form like citrate or oxide to one that is gentler on the stomach, such as glycinate or malate.
Stay hydrated: If you experience diarrhea, it is vital to drink plenty of fluids to prevent dehydration.

Conclusion

While magnesium is a critical mineral for overall health, it's important to be aware of what are the side effects of magnesium supplements, which can range from mild digestive issues to severe toxicity in rare cases. Being mindful of the type and dosage of your supplement, especially for those with pre-existing conditions or on medication, is crucial. Always consult a healthcare professional before beginning a new supplement regimen to ensure it is right for your individual health needs. Information from reliable sources, such as the NIH Office of Dietary Supplements, is a valuable resource for making informed health decisions.

Frequently Asked Questions

The most common side effect is gastrointestinal distress, which can include diarrhea, nausea, and stomach cramps. This is particularly likely with higher doses and less absorbable forms of magnesium.

Forms of magnesium with a laxative effect, such as magnesium oxide and magnesium citrate, are most likely to cause diarrhea. These draw water into the intestines, softening stool and stimulating bowel movements.

Yes, while the kidneys typically regulate levels, taking excessive amounts of supplemental magnesium, especially over 350 mg per day, can lead to magnesium toxicity (hypermagnesemia).

People with impaired kidney function or chronic kidney disease are at the highest risk for magnesium toxicity, as their kidneys are unable to effectively excrete excess magnesium.

To avoid digestive issues, start with a low dose, take your supplement with food, consider splitting the dose, and use a well-tolerated form like magnesium glycinate.

Yes, magnesium can interact with certain medications, including some antibiotics, diuretics, bisphosphonates, and blood pressure medications. Always consult your doctor or pharmacist about potential interactions.

Severe symptoms of a magnesium overdose include muscle weakness, lethargy, low blood pressure, and, in very rare and extreme cases, irregular heartbeats or cardiac arrest.