Toothpastedog, funnily enough I use Magnesium Oxide as needed (the worst type of Magnesium supplement) purely as a laxative for constipation caused by opiates, processed carbs, high protein intake, or by Magnesium glycinate.
Magnesium actually causes constipation, it's all that non-chelated Mg+ (broken off from MgO in the case of Magnesium Oxide) in subpar Magnesium supplements that float around in your stomach and bowels, waiting to be bound to free-floating ions from water that causes diarrhea from the osmotic laxative effect. Mg+ doesn't make it to your intestines with out binding to water ions.
Chelated minerals are the way to go, they are bound to chelating agents, such as amino acids, so they are purely absorbed by the intestines.
Btw, Madog is our resident BLUA and search engine Nazi, you'll get used to her soon enough.