Why Can't I Tolerate Magnesium? Understanding Supplement Sensitivity

September 23, 2025 •

4 min read

An estimated 50% of the US population consumes less than the required amount of magnesium, but not everyone tolerates supplements well. If you've been asking why can't I tolerate magnesium, the reasons often relate to the specific form you're taking, the dosage, or your body's unique digestive sensitivity.

Quick Summary

Magnesium intolerance is often caused by low-bioavailability forms like magnesium oxide, which pull water into the intestines and cause digestive distress. High doses, certain health conditions, and sensitive GI tracts also contribute to adverse reactions, but switching to a gentler form can often help.

Key Points

Bioavailability matters: Poorly absorbed magnesium forms, like magnesium oxide, are the most common cause of digestive intolerance due to their laxative effect.
Switch forms for relief: Choosing highly bioavailable forms such as magnesium glycinate or malate can drastically reduce or eliminate gastrointestinal side effects.
Dosage is critical: Starting with a low dose and increasing it slowly helps your body adapt and prevents overwhelming your digestive system, regardless of the supplement form.
Listen to your body: Some individuals have pre-existing GI sensitivities that make them more prone to side effects from any supplement, necessitating a more cautious approach.
Food is the safest source: Increasing magnesium intake through whole foods like leafy greens, nuts, and seeds is the most natural way to boost levels without adverse effects.

Understanding Magnesium Bioavailability

Not all magnesium supplements are created equal. The key difference lies in their bioavailability, which is the amount of magnesium your body can absorb and utilize. Some forms are poorly absorbed, meaning a large portion of the mineral is left in the digestive tract. This unabsorbed magnesium acts as an osmotic agent, drawing water into the intestines and leading to side effects like diarrhea, loose stools, and abdominal cramping. It's a common reason people feel they simply can't tolerate magnesium.

The Problem with Poorly Absorbed Forms

One of the most common culprits for poor tolerance is magnesium oxide. While it contains a high concentration of elemental magnesium, its absorption rate is notoriously low. This makes it effective as a laxative but often unsuitable for long-term daily supplementation intended to increase systemic magnesium levels. Many of the most affordable, widely available supplements use this form, which can explain why many first-time users experience negative side effects and conclude that magnesium is not for them.

Different Forms and Their Impact on Your Gut

Choosing the right form of magnesium is crucial for minimizing side effects. While magnesium oxide is harsh on the digestive system, other forms offer superior absorption and gentler digestion. For those with sensitive stomachs or pre-existing gastrointestinal conditions, these alternatives can be a game-changer.

Magnesium Glycinate: This form is bound to the amino acid glycine, which makes it highly absorbable and gentle on the stomach. It's often recommended for people seeking muscle relaxation and sleep support without the laxative effect.
Magnesium Malate: Malate is an organic acid involved in energy production. When combined with magnesium, it creates a well-absorbed form that is less likely to cause digestive upset. It is often favored by those looking to support muscle function and energy levels.
Magnesium Citrate: A very popular form, magnesium citrate has moderate bioavailability. While it's better absorbed than oxide, it can still have a mild laxative effect, especially at higher doses. It's a good option for those who need a gentle stool softener.
Magnesium L-Threonate: This form is particularly known for its ability to cross the blood-brain barrier, making it effective for cognitive support. It is generally well-tolerated and does not typically cause gastrointestinal issues.

The Role of Dosage and Individual Sensitivity

Even with highly absorbable forms, taking too much too quickly can overwhelm the digestive system. A sudden increase in magnesium intake can trigger a laxative effect, regardless of the supplement type. This is why starting with a low dose and gradually increasing it is a key strategy for improving tolerance. Additionally, some individuals have naturally more sensitive digestive tracts. Conditions such as Irritable Bowel Syndrome (IBS) or other inflammatory bowel diseases can make a person more susceptible to magnesium's side effects. For these individuals, a food-first approach or consultation with a healthcare provider is especially important.

A Comparison of Magnesium Forms


Feature	Magnesium Oxide	Magnesium Citrate	Magnesium Glycinate	Magnesium Malate
Bioavailability	Very Low	Moderate	High	High
Laxative Effect	High	Moderate	Low	Low
Cost	Low	Moderate	Higher	Higher
Best For	Constipation relief	General use, moderate effect	Sensitive stomachs, relaxation	Energy, muscle support

How to Improve Magnesium Tolerance

If you've had a bad experience with magnesium, don't give up entirely. Several strategies can help you find a supplement that works for you.

Start with a Low Dose: Begin with the smallest possible dose, perhaps even half of the recommended serving, and take it with food. This allows your body to adjust gradually.
Switch Forms: As detailed above, changing from a poorly absorbed form like oxide to a gentler, more bioavailable option like glycinate or malate can eliminate side effects completely.
Consider Timing: Some people find that taking their magnesium supplement with a meal helps mitigate stomach upset. Others prefer taking it in the evening, as its relaxing effects can aid sleep.
Prioritize Food Sources: The safest and most bioavailable source of magnesium is often whole foods. Incorporating more leafy greens, nuts, seeds, and legumes can boost your intake naturally without the risk of GI side effects. A food-first approach is always a great place to start.
Consult a Healthcare Provider: If you have persistent issues or an underlying health condition, speaking with a doctor or registered dietitian is vital. They can assess your needs and recommend the most appropriate form and dosage. For more information on the role of magnesium in health, see resources from the National Institutes of Health.

Conclusion

Finding that you can't tolerate magnesium is a common and frustrating experience, but it doesn't mean you must abandon your health goals. By understanding the differences between supplement forms, adjusting your dosage, and considering your body's unique sensitivities, you can find a magnesium solution that provides the benefits you seek without the unwanted side effects. The key is to be patient, strategic, and willing to experiment with different options under informed guidance.

Frequently Asked Questions

For those with a sensitive stomach, magnesium glycinate is typically the best choice. It is bound to the amino acid glycine, making it highly absorbable and gentle on the digestive tract with minimal to no laxative effect.

No, magnesium does not always cause diarrhea. The laxative effect is primarily associated with poorly absorbed forms like magnesium oxide and is also dependent on the dosage. Gentler, more bioavailable forms are much less likely to cause this side effect.

Yes, it is possible to get enough magnesium from food. Many whole foods are rich in magnesium, including spinach, almonds, pumpkin seeds, black beans, and avocados. Prioritizing these foods can help you increase your intake naturally.

If you experience side effects, try lowering your dose, switching to a more bioavailable form like glycinate or malate, or taking your supplement with a meal. Consulting a healthcare provider is recommended if issues persist.

Yes, some medications, including certain antibiotics, diuretics, and heart medications, can interact with magnesium. It is crucial to speak with a healthcare provider before taking any new supplement, especially if you are on medication.

Yes, conditions such as Irritable Bowel Syndrome (IBS), Crohn's disease, and other digestive disorders can increase an individual's sensitivity to magnesium supplements. Kidney disease can also affect how your body processes magnesium.

If you are concerned about your magnesium levels, a blood test can be performed by a healthcare provider. However, since most magnesium is stored in the bones and cells, a blood test may not always give a complete picture. A provider can help interpret the results in the context of your overall health.