Does magnesium cause diarrhea? Are some forms less likely to cause loose stools than others?

Answer:

Taking too much magnesium from a supplement in amounts that exceed the Tolerable Upper Intake Level (the "UL") for magnesium can cause diarrhea. Magnesium that occurs naturally in foods does not cause this. Supplements should only be used to help you get to your requirement.

If you must take a high amount of magnesium for medical reasons, certain forms are less likely to cause diarrhea than others. Forms that are absorbed well by the body — such as magnesium chloride, bisglycinate, and glycerophosphate — are less likely to have a laxative effect, although all forms of magnesium can cause loose stools or diarrhea in high enough amounts. Magnesium citrate, gluconate, aspartate, and lactate may be appropriate at low doses but can have laxative effects at higher doses. Forms that are not absorbed well — such as magnesium hydroxide, carbonate, oxide and sulfate — are likely to have laxative effects and are more appropriate for relieving constipation.

For details, see the Dosing and how to take and the Choosing the right form of magnesium sections of our Magnesium Supplements Review. Also see our Top Picks among products — covering moderate-dose as well as high-dose magnesium (in the form less likely to cause diarrhea) based on our independent laboratory tests of products.