You are taking too much magnesium from a supplement, and diarrhea is known side effect of exceeding the Upper Tolerable Intake Level (the "UL") for magnesium when taken as a supplement. 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. 

For details see the Dosing and how to take section 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).

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April 19, 2020

Which foods are high in magnesium? I cant take a supplement because of the laxative affect. And Ive tried different levels of milligrams.
April 20, 2020

Hi Stephen - Please see the ConsumerTips section of the Magnesium Review for a list of foods that are good sources of magnesium

May 16, 2018

I had that same problem. When I had an evaluation by an alternative nutritionist I was told that certain forms of magnesium cause diarrhea. I was advised to take magnesium glycinate. Have been supplementing with that form for years now and never had the same problem.

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