Does Magnesium Make You Feel Dehydrated? Understanding the Risk

December 21, 2025 •

4 min read

While magnesium is a vital electrolyte that helps regulate fluid balance in the body, certain high-dose supplements, particularly magnesium citrate and oxide, can trigger a laxative effect leading to fluid loss. This surprising consequence is why understanding the type and dosage of your magnesium supplement is crucial for maintaining proper hydration.

Quick Summary

The link between magnesium and hydration is complex; while essential for fluid balance, some forms of magnesium can cause dehydration at high doses. The osmotic effect in the intestines draws water from the body, potentially leading to diarrhea and electrolyte imbalance. Careful dosage and selecting the right type of magnesium are key to avoiding unwanted side effects and staying hydrated.

Key Points

Dose Matters: High supplemental doses of magnesium, especially above 350 mg, can cause a laxative effect and lead to dehydration.
Form is Critical: Certain forms, like magnesium citrate and oxide, are more likely to cause diarrhea and fluid loss due to their osmotic properties.
Gentler Alternatives: Forms such as magnesium glycinate and malate are better absorbed and less likely to cause digestive issues and dehydration.
Individual Factors: Your risk of dehydration is influenced by your overall hydration status, kidney health, and daily supplement dosage.
Preventive Measures: To avoid dehydration, choose a highly absorbable form, start with a low dose, split the dosage throughout the day, and drink plenty of water.
Electrolyte Importance: While some magnesium can dehydrate, the mineral itself is an essential electrolyte for regulating overall fluid balance in the body.

The Dual Role of Magnesium: Hydration and Dehydration

Magnesium is an essential mineral involved in over 300 biochemical reactions in the human body, from nerve function to muscle control and energy production. As a key electrolyte, it works in concert with sodium and potassium to regulate the movement of fluids inside and outside of cells, which is fundamental to maintaining proper hydration. In fact, an adequate intake of magnesium is vital for preventing muscle cramps and other signs of dehydration, especially during exercise.

However, the relationship between magnesium and hydration is more nuanced. While a deficiency can impair the body’s ability to hydrate effectively, an excessive intake—particularly from certain supplements—can paradoxically lead to dehydration. This is because unabsorbed magnesium creates an osmotic effect in the digestive tract, drawing water from the body into the intestines. This influx of water can result in diarrhea, which, if persistent, causes significant fluid and electrolyte loss, increasing the risk of dehydration.

How Specific Magnesium Forms Influence Fluid Balance

Not all magnesium supplements are created equal, and their chemical form significantly impacts their potential to cause dehydration. The bioavailability of a supplement—how well the body can absorb and use it—is the key factor. Forms with low bioavailability often leave more unabsorbed magnesium in the gut, leading to a greater osmotic and laxative effect.

Magnesium Forms Most Likely to Cause Dehydration

Magnesium Citrate: Known for its excellent solubility and high bioavailability when used appropriately, magnesium citrate is also a popular saline laxative used to treat constipation. In high doses, its water-drawing properties are pronounced, making diarrhea and subsequent dehydration a significant risk.
Magnesium Oxide: This is one of the most common and inexpensive forms of magnesium, often found in supplements and antacids. However, its bioavailability is quite low, meaning a large portion of the magnesium remains unabsorbed in the gut. This makes it more likely to cause gastrointestinal side effects like diarrhea, especially at higher doses.

Magnesium Forms Less Likely to Cause Dehydration

Magnesium Glycinate: This form is chelated with the amino acid glycine, which is thought to enhance absorption and reduce the likelihood of digestive upset. Many people find it gentler on the stomach, making it a good choice for those prone to diarrhea.
Magnesium Malate: Combining magnesium with malic acid, this form is also generally well-tolerated by the digestive system. It has a high absorption rate, similar to glycinate, making it less likely to cause unwanted laxative effects.

Comparison of Common Magnesium Forms


Magnesium Form	Primary Use	Potential for Dehydration	Bioavailability	Common Side Effects
Magnesium Citrate	Constipation relief, supplement	High, especially at high doses	Medium-High	Diarrhea, cramping, nausea
Magnesium Oxide	Antacid, supplement	High, due to poor absorption	Low	Diarrhea, stomach upset
Magnesium Glycinate	Relaxation, sleep, supplement	Low	High	Minimal digestive issues
Magnesium Malate	Energy, muscle support, supplement	Low	High	Minimal digestive issues

Factors Increasing Dehydration Risk with Magnesium

Several individual factors can amplify the risk of dehydration when taking magnesium supplements:

Dosage: Exceeding the recommended dosage, particularly the Tolerable Upper Intake Level (UL) of 350 mg per day for supplemental magnesium, dramatically increases the risk of side effects like diarrhea. The higher the dose, the more unabsorbed magnesium is present in the gut to cause an osmotic effect.
Existing Hydration Status: If you are already under-hydrated before taking a supplement, the fluid-shifting effects of magnesium will have a more pronounced impact on your overall hydration levels.
Kidney Function: Individuals with impaired kidney function should exercise extreme caution with magnesium supplementation, as their bodies may have difficulty excreting excess magnesium, leading to toxicity and related complications like dehydration.
Health Conditions: Diarrhea from magnesium can exacerbate other conditions that cause fluid loss, such as chronic illness or other gastrointestinal issues.

How to Prevent Dehydration When Taking Magnesium

For individuals supplementing with magnesium, a proactive approach can mitigate the risk of dehydration. You can ensure you maintain healthy hydration levels by taking a few key steps:

Choose a well-absorbed form: Opt for forms like magnesium glycinate or malate, which are less likely to cause digestive upset compared to citrate and oxide.
Start with a lower dose: Begin with a smaller dose to see how your body reacts before increasing it. This allows your system to adjust and helps you find the optimal amount without triggering side effects.
Split your daily dosage: If you need a higher intake, divide it into smaller doses throughout the day instead of taking it all at once. This approach improves absorption and is gentler on your digestive system.
Take with food: Ingesting magnesium with a meal can improve absorption and reduce the likelihood of stomach irritation. A balanced meal with healthy fats, protein, and carbohydrates can further aid uptake.
Stay adequately hydrated: Regardless of supplementation, consistently drinking enough water is paramount. Be extra vigilant about your fluid intake, especially if you notice increased urination or changes in bowel movements.
Consult a healthcare professional: Before starting any new supplement regimen, especially if you have pre-existing health conditions like kidney issues, it is essential to speak with a doctor.

Conclusion

While magnesium is a critical component of a healthy hydration system, it can indeed make you feel dehydrated under certain conditions. The risk is predominantly linked to specific supplement forms, like citrate and oxide, and excessive dosages that cause a strong osmotic laxative effect. However, by selecting gentler, more bioavailable forms, starting with a low dose, and ensuring you maintain adequate hydration, you can safely enjoy the benefits of magnesium supplementation without experiencing unwanted side effects. Always listen to your body and consult a healthcare provider with any persistent concerns. For more information on electrolytes, visit the NCBI Bookshelf.

Frequently Asked Questions

Yes, high doses of certain magnesium supplements, particularly magnesium citrate and oxide, can cause diarrhea. This fluid loss can lead to dehydration if not managed with increased fluid intake.

Magnesium glycinate and magnesium malate are generally better tolerated and less likely to cause digestive issues. They are more bioavailable, meaning the body absorbs them more efficiently, reducing the osmotic effect in the intestines.

Magnesium can act as an osmotic agent, drawing water from the body into the intestines. This effect, especially with poorly absorbed forms or high doses, can result in diarrhea, which leads to fluid and electrolyte loss and dehydration.

Symptoms can include dry mouth, increased thirst, decreased urination, dark-colored urine, fatigue, dizziness, and light-headedness. These are common signs of fluid loss that should not be ignored.

The Tolerable Upper Intake Level (UL) for supplemental magnesium is 350 mg per day for healthy adults. Exceeding this amount without medical supervision increases the risk of side effects, including diarrhea and dehydration.

Yes, magnesium is a key electrolyte for regulating fluid balance. A deficiency can cause an electrolyte imbalance that may disrupt the body's ability to maintain proper hydration and lead to issues like muscle cramps.

If you experience diarrhea, consider lowering your dose or splitting it throughout the day. You may also want to switch to a more bioavailable form, like glycinate. Most importantly, increase your fluid intake and consult a healthcare professional if symptoms persist.