May mask internal bleeding symptoms secondary to NSAIDs. Avoid concomitant use w/ tetracycline, quinolones, propranolol, atenolol, captopril, ranitidine, famotidine & aspirin. Al may cause nausea, vomiting & constipation; risk of osteomalacia in patients w/ low phosphate diet. Hypermagnesaemia may occur w/ impaired renal function. Mg hydroxide & other Mg salts may cause CNS depression w/ renal insufficiency; may cause diarrhea potentially leading to dehydration.