Magnesium Oxide Mechanism of Action of Magnesium Oxide This medication is a mineral supplement used to prevent and treat low amounts of magnesium in the blood. Magnesium is very important for the normal functioning of cells, nerves, muscles, bones, and the heart. Hypomagnesia may be produced by treatment with "water pills" (diuretics such as furosemide, hydrochlorothiazide), a poor diet, alcoholism, or other medical conditions (e.g., severe diarrhea/vomiting, stomach/intestinal absorption problems, poorly controlled diabetes).It is also used to prevent hyperacidity as a gastric acid nutraliser.