Can taking magnesium supplements cause diarrhea?

December 18, 2025 •

4 min read

Over half of Americans may not get enough magnesium from their diet, but turning to supplements can sometimes cause an unintended side effect. The question of whether taking magnesium supplements can cause diarrhea is frequently asked by new users.

Quick Summary

Magnesium supplements can cause diarrhea, with the likelihood depending on the dose and specific form. This occurs because unabsorbed magnesium draws water into the intestines, acting as a laxative. Some forms are gentler than others.

Key Points

Dose Dependence: Higher doses of magnesium supplements are more likely to cause diarrhea due to increased amounts of unabsorbed mineral in the gut.
Osmotic Effect: Diarrhea from magnesium is caused by an osmotic effect, where unabsorbed magnesium draws water into the intestines, softening stools.
Form Matters: Certain forms, like magnesium citrate and oxide, are more prone to causing diarrhea due to lower bioavailability, while forms like glycinate are gentler.
Prevention Strategies: To prevent diarrhea, start with a low dose, take supplements with food, and divide doses throughout the day.
Gentler Alternatives: Switching from poorly absorbed forms to more bioavailable ones, such as magnesium glycinate, can reduce digestive side effects.
Dietary vs. Supplemental: It is rare to get diarrhea from dietary sources of magnesium, as kidneys regulate excess mineral from food more efficiently than from high-dose supplements.
When to Seek Help: Persistent or severe diarrhea, or symptoms of toxicity like muscle weakness or low blood pressure, requires immediate medical consultation.

The Osmotic Mechanism Behind Magnesium-Induced Diarrhea

Magnesium is an essential mineral vital for hundreds of bodily functions, including muscle and nerve function, blood pressure regulation, and bone health. When taken as a supplement, especially in higher doses, not all of the magnesium is absorbed by the small intestine. The unabsorbed magnesium salts remain in the gastrointestinal tract, where they create an osmotic gradient. This process draws water from the surrounding tissues into the intestines, softening the stool and increasing its volume. This influx of water and electrolytes accelerates intestinal transit, leading to loose stools or, in some cases, outright diarrhea. This same mechanism is precisely why magnesium compounds like magnesium citrate are used therapeutically as laxatives for constipation.

The Impact of Dose and Formulation

The amount of magnesium you take is a primary factor in whether you will experience diarrhea. Higher doses are more likely to cause this side effect, which is why the tolerable upper intake level (UL) for supplemental magnesium is set at 350 mg for adults. However, it's not just the quantity that matters. The specific form, or formulation, of the magnesium supplement plays a critical role in its bioavailability and potential for causing digestive distress. Some forms are more easily absorbed by the body, meaning less unabsorbed magnesium is left in the gut to cause a laxative effect. Other, less bioavailable forms are notorious for causing diarrhea.

Comparison of Magnesium Forms and Diarrhea Risk


Form of Magnesium	Bioavailability	Diarrhea Risk	Common Use
Magnesium Citrate	High	High	Often used as a laxative.
Magnesium Oxide	Low	High	Used as an antacid and potent laxative.
Magnesium Glycinate	High	Low	Gentler on the stomach; often recommended for sleep and relaxation.
Magnesium Malate	High	Low	Well-absorbed and often recommended for energy and muscle function.
Magnesium Sulfate	Varies	High	Used topically (Epsom salts) and orally as a laxative.
Magnesium Lactate	High	Low	Gentle on the digestive system.

Strategies to Prevent and Manage Diarrhea

If you find that your magnesium supplement is causing digestive discomfort, several strategies can help mitigate the side effects without giving up the benefits of the mineral:

Start with a low dose: Begin with a smaller dose than the label recommends and gradually increase it over time to allow your body to adjust.
Divide your doses: Instead of taking a single large dose, split it into smaller portions throughout the day. This reduces the amount of unabsorbed magnesium in the gut at any one time.
Take with food: Taking your supplement with a meal can slow absorption and may reduce the risk of diarrhea.
Switch to a gentler form: If you are taking a form like citrate or oxide and experiencing issues, consider switching to a more bioavailable and gentle form like glycinate or malate.
Stay hydrated: Diarrhea can lead to dehydration, so it's important to drink plenty of water and replenish electrolytes if you have loose stools.

When to Consult a Doctor

While mild, temporary diarrhea from magnesium supplements is generally not a cause for concern, persistent or severe diarrhea warrants medical attention. If you experience any of the following symptoms, stop taking the supplement and contact a healthcare professional immediately:

Rectal bleeding.
Diarrhea that lasts for more than a week.
Signs of magnesium toxicity, such as low blood pressure, muscle weakness, fatigue, facial flushing, or an irregular heartbeat.
No bowel movement occurs after using magnesium as a laxative. These symptoms can indicate a more serious condition, especially for individuals with pre-existing health issues like kidney disease, who are at higher risk for magnesium buildup.

Conclusion

In summary, yes, taking magnesium supplements can cause diarrhea, especially if you are taking high doses or using certain forms like magnesium citrate or oxide. This is due to an osmotic effect in the intestines. For most people, this side effect can be prevented or managed by adjusting the dose, splitting intake throughout the day, and choosing a more easily absorbed form like magnesium glycinate. However, those with pre-existing conditions or experiencing severe or prolonged symptoms should consult a healthcare provider for personalized guidance and to rule out other issues. It's crucial to always listen to your body and make informed choices about your supplements.

For more information on magnesium, you can visit the Office of Dietary Supplements website from the National Institutes of Health.

A Note on Dietary Magnesium

It is extremely rare to experience diarrhea from consuming magnesium through food alone. Your kidneys are highly effective at filtering out excess magnesium from food sources. The problem of digestive upset is almost exclusively tied to supplemental forms and high dosages. Incorporating magnesium-rich foods like leafy greens, nuts, seeds, and whole grains into your diet is always the safest way to increase your intake.

Frequently Asked Questions

Magnesium citrate and magnesium oxide are the forms most likely to cause diarrhea because they are less bioavailable and act as osmotic laxatives.

Magnesium glycinate is considered one of the best forms to take to avoid diarrhea. It is more bioavailable and gentler on the digestive system.

You can reduce the laxative effect by lowering your dose, splitting it into smaller doses throughout the day, or taking it with food.

It is highly unlikely to experience diarrhea from magnesium obtained through food alone. Your kidneys effectively regulate excess mineral from dietary sources.

Doses exceeding the tolerable upper intake level of 350 mg from supplements are more likely to cause diarrhea, though individual tolerance varies.

If diarrhea is mild and temporary, you can try adjusting your dose or switching forms. However, if it is persistent, severe, or accompanied by other serious symptoms, you should stop and consult a doctor.

Magnesium citrate is a fast-acting osmotic laxative, typically producing a bowel movement within 30 minutes to 6 hours.