Why Magnesium Supplements Can Cause Diarrhea + How To Find One That Won't

It's estimated that 48% of the U.S. population1 doesn't get enough magnesium from diet alone. This is an issue since magnesium is a critical nutrient that plays a role in everything from blood sugar to sleep quality. Targeted magnesium supplements can help fill this dietary gap.

There are a few common forms of magnesium supplements, and while they are generally safe to use, some of them can cause a rather unpleasant side effect in certain individuals: diarrhea.

The issue really boils down to too much unabsorbed magnesium, which attracts water from surrounding tissues in the intestine or colon and overstimulates the bowel.

"In higher doses, magnesium can interfere with the smooth muscles of the intestines, causing stimulation of the gut or some relaxation/disruption of the normal peristalsis," explains double board-certified surgeon and author Kent Sasse, M.D. "The result is diarrhea and sometimes cramping pain."

The key to avoiding diarrhea is twofold. You need to ensure you're taking the right kind of magnesium for your needs and nailing the dosage so your body can absorb it completely. "In general, the higher the dose, the more likely a person is to experience diarrhea," says Sasse.

If you're taking oral supplements of magnesium forms like citrate, malate, glycinate, and oxide, it's important to follow recommended daily doses. According to the National Institute of Health, the tolerable upper intake level for supplemental magnesium is as follows:

Dosing aside, certain versions of magnesium supplements are also more likely to cause diarrhea than others.

"Some forms of magnesium supplements, such as carbonate, chloride, gluconate, oxide, and citrate form salts that draw water into the gut, leading to diarrhea—an osmotic effect of the magnesium salt," explains Sasse.

Magnesium citrate is one of the most common forms, and research suggests2 it has one of the highest bioavailability (absorbability). But it has a natural laxative effect and is often used to treat constipation. The same is true of magnesium oxide—the main ingredient in milk of magnesia, an over-the-counter medication for constipation relief.

If you're considering a magnesium supplement and you'd like to avoid the possibility of diarrhea, a chelated version like magnesium glycinate is the place to start. It's designed to be gentle on the GI tract.

It's a form of magnesium that's bound to an organic compound—in this case, glycine, an amino acid—making it easily absorbed in the body.

That being said, it's a good idea to try different forms of the supplement to find what works for you.

"Some people may find different kinds of the supplement to be gentler," notes Sasse, "and it's worth experimenting since everyone is different."

Boosting your body's intake of magnesium can pay off with better sleep, and less stress, among other benefits. And while it's true that diarrhea can be an unpleasant side effect, you can minimize the chances with proper dosing and by opting for a form of magnesium that's gentler on the body.