Uses of Ferrous Fumarate Tablets and Capsules: It is used to aid diet needs. It is used to treat or prevent low iron in the body. How is this medicine (Ferrous Fumarate Tablets and Capsules) best taken? Use this medicine (ferrous fumarate tablets and capsules) as ordered by your doctor. Read all information given to you. Follow all instructions closely. This medicine works better if you take it on an empty stomach. You may take this medicine with food if it causes an upset stomach. Some foods like eggs, whole grain breads, cereal, dairy products, coffee, and tea may make this medicine (ferrous fumarate tablets and capsules) not work as well. If this medicine causes an upset stomach, talk with your doctor about the best way to take this medicine (ferrous fumarate tablets and capsules) with food. Take with a full glass of water. If antacids are used, they may need to be taken at some other time than this medicine. Talk with your doctor or pharmacist. What are some other side effects of Ferrous Fumarate Tablets and Capsules? All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away: Belly pain. Loose stools (diarrhea). Hard stools (constipation). Change in color of stool to green. Not hungry. Upset stomach or throwing up. Stomach cramps.