Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using magnesium oxide and call your doctor at once if you have:
rectal bleeding;
coughing up blood or vomit that looks like coffee grounds;
bloody or tarry stools; or
no bowel movement after using magnesium oxide as a laxative.
Common side effects may include:
diarrhea; or
upset stomach.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Magnesium oxide side effects (more detail)
