Iron deficiency anemia induced by magnesium overuse: a case report.

Although in vitro studies show that iron absorption can be inhibited by magnesium laxatives such as magnesium oxide, taking oral iron supplements with magnesium laxatives is not considered a clinical problem.A 28-year-old woman diagnosed with anorexia nervosa who overused magnesium laxatives was admitted to our hospital to evaluate her refractory iron deficiency anemia (IDA), despite having taken oral iron replacement therapy for nine months. She had had amenorrhea for years and her fecal occult blood tests were negative. Furthermore, upper gastrointestinal endoscopy showed no suspected gastroduodenal bleeding or gastroenteritis. We considered her IDA to be induced by malabsorption of iron due to magnesium laxative overuse. Psychoeducational intervention stopped the overuse and oral iron replacement therapy was switched to the intravenous route. During outpatient follow-up, her anemia gradually improved; however, when her magnesium laxative overuse began again, her hemoglobin levels suddenly decreased.Clinicians should be attentive to the interactions between iron and magnesium laxatives.