Magnesium oxide treats low levels of magnesium in the blood, indigestion, and incomplete or infrequent bowel movements, according to WebMD. This mineral supplement is particularly used for patients who have conditions that cause excessive magnesium loss.
Conditions that cause magnesium deficiency include a poor diet, alcoholism, treatment with diuretics, poorly controlled diabetes, and stomach or intestinal absorption problems, explains WebMD. Severe diarrhea, vomiting and other health conditions also cause magnesium to be lost faster than it is replaced. In an otherwise healthy individual, sufficient magnesium is generally provided through a well-balanced diet. Magnesium is necessary for muscles, bones, nerves, the heart and cells to function properly.