Exploring the Negative Side Effects of Magnesium Supplementation

December 28, 2025 •

3 min read

Gastrointestinal issues like diarrhea and nausea are the most commonly reported side effects of magnesium supplementation, especially with doses over 350 mg. These effects can range from mild and inconvenient to a sign of a more serious issue like toxicity, depending on the dosage and individual health factors.

Quick Summary

Magnesium supplements can cause digestive issues, and high doses may lead to toxicity, especially for those with kidney problems. Awareness of different magnesium forms and proper dosage helps minimize adverse effects.

Key Points

Digestive Upset: High doses of magnesium, especially forms like oxide and citrate, commonly cause diarrhea, nausea, and cramping.
Toxicity is Rare: Serious magnesium toxicity (hypermagnesemia) is rare but can occur from excessive supplementation, especially in those with impaired kidney function.
Kidney Health is Key: Individuals with chronic kidney disease are at significantly higher risk for magnesium accumulation and toxicity because their kidneys cannot excrete excess mineral effectively.
Form Matters: Magnesium glycinate and malate are generally better tolerated and less likely to cause digestive side effects compared to forms like magnesium oxide or citrate.
Drug Interactions: Magnesium can interact with several medications, including certain antibiotics, diuretics, and bisphosphonates, potentially affecting their absorption or efficacy.
Consult a Doctor: Before starting magnesium supplements, especially high-dose ones, it is crucial to consult a healthcare provider to ensure safety and prevent adverse effects.

Common Gastrointestinal Side Effects

Even at moderate doses, magnesium supplements can trigger uncomfortable digestive symptoms. This is because unabsorbed magnesium salts in the intestines draw water into the colon, which has a natural laxative effect. Common issues include:

Diarrhea: The most frequent complaint, often dose-dependent. Higher doses increase the osmotic effect, leading to looser stools.
Nausea and Vomiting: Some individuals experience stomach upset, especially when taking magnesium on an empty stomach.
Stomach Cramps: Abdominal cramping can accompany the laxative effect, particularly with poorly absorbed forms.

Serious Side Effects and Magnesium Toxicity

While rare in healthy individuals, magnesium toxicity, also known as hypermagnesemia, can occur from very high doses of supplements or medications containing magnesium. This is a serious condition that can lead to severe complications. Symptoms often develop when serum magnesium concentrations exceed 1.74–2.61 mmol/L.

Symptoms of moderate to severe magnesium toxicity include:

Hypotension: Dangerously low blood pressure.
Muscle Weakness: Severe fatigue and generalized muscle weakness, which can progress to paralysis.
Lethargy and Confusion: Mental state changes, including drowsiness and depression.
Respiratory Distress: In extreme cases, muscle paralysis can affect the diaphragm, leading to difficulty breathing.
Cardiac Issues: Irregular heartbeats, which can progress to cardiac arrest in the most severe cases.

Risk Factors for Increased Side Effects

Certain individuals are at a higher risk of experiencing negative side effects from magnesium, especially hypermagnesemia. It is crucial for these groups to consult a healthcare provider before taking any supplement.

Impaired Kidney Function

The kidneys are responsible for filtering excess magnesium from the body. When kidney function is compromised, this process is inefficient, allowing magnesium to build up to toxic levels. This includes patients with chronic kidney disease (CKD) or those on dialysis.

High-Dose Supplementation

Taking very high-dose magnesium supplements, or using magnesium-containing laxatives and antacids excessively, significantly increases the risk of toxicity. The Tolerable Upper Intake Level (UL) for supplemental magnesium for adults is 350 mg per day, though some medical conditions may warrant higher doses under supervision.

Older Adults

Elderly individuals may be at a higher risk of both magnesium deficiency and toxicity. Reduced kidney function and a higher likelihood of taking interacting medications increase their vulnerability.

Magnesium Supplement Forms and Tolerability

Not all magnesium supplements are created equal, and the chemical form can significantly impact absorption and side effects.

Comparison of Common Magnesium Forms


Magnesium Form	Common Use	Bioavailability	Likelihood of Diarrhea
Magnesium Oxide	Multivitamins, antacids	Poorly absorbed	High
Magnesium Citrate	Oral laxative, deficiency	Well absorbed	High, especially at high doses
Magnesium Glycinate	Relaxation, deficiency	High, less harsh on stomach	Low, gentle on digestion
Magnesium Malate	Energy, deficiency	High	Low
Magnesium Sulfate	Epsom salts (topical), cathartic	Variable (oral), low (topical)	High (oral)

Drug Interactions with Magnesium

Magnesium can interact with various medications, altering their absorption or effects. Taking magnesium at least 2 hours apart from these medications is often recommended.

Antibiotics: Magnesium can form insoluble complexes with certain antibiotics, including tetracyclines (e.g., doxycycline) and quinolones (e.g., ciprofloxacin), reducing their effectiveness.
Bisphosphonates: Used for osteoporosis, bisphosphonate absorption can be decreased by magnesium.
Diuretics: Some diuretics, like furosemide, can increase magnesium excretion, while potassium-sparing diuretics can increase magnesium levels.
Proton-Pump Inhibitors (PPIs): Long-term use of PPIs can lead to reduced magnesium absorption.
Calcium Channel Blockers: Co-administration with magnesium can cause a dangerously low drop in blood pressure.

Conclusion: Navigating Magnesium Safely

While magnesium is essential for numerous bodily functions and supplementation can be beneficial, it is not without potential negative effects. Mild digestive issues like diarrhea are common, but serious toxicity is a rare risk, primarily for those with impaired kidney function or those taking extremely high doses. The form of magnesium, dosage, and a person's individual health profile all play a crucial role in mitigating these risks.

To ensure safe supplementation, it is recommended to start with a low dose, consider a more bioavailable and gentle form like glycinate or malate, and take supplements with food. Most importantly, consult a healthcare provider before starting any new supplement, especially if you have an existing health condition or take other medications.

For more detailed information on magnesium, consult the NIH Office of Dietary Supplements.

Frequently Asked Questions

The most common side effect of magnesium supplementation is diarrhea, which is particularly associated with higher doses and less-absorbable forms like magnesium oxide and citrate.

It is extremely rare to get too much magnesium from dietary sources alone. For healthy individuals, the kidneys effectively filter and excrete any excess magnesium from food.

Individuals with impaired kidney function, such as those with chronic kidney disease, are at the highest risk for magnesium toxicity because their bodies cannot efficiently remove excess magnesium.

Signs of a serious magnesium overdose (hypermagnesemia) can include low blood pressure, muscle weakness, confusion, irregular heartbeat, and difficulty breathing.

If you experience diarrhea, you can try lowering your dose, switching to a more gentle form like magnesium glycinate, or taking the supplement with food. If the issue persists, consult your doctor.

Yes, the type of magnesium can affect side effects. Poorly absorbed forms like magnesium oxide and citrate are more likely to cause gastrointestinal issues, while better-absorbed forms like glycinate are typically gentler on the stomach.

Yes, magnesium can interact with various medications, including certain antibiotics, diuretics, and bisphosphonates. It's recommended to space out the timing of your supplement and other medications.