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. “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: “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. 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.”
