Ferrous sulfate is an iron supplement used to treat or prevent low blood levels of iron (e.g., for iron deficiency anemia or during pregnancy). Iron is an important mineral that the body needs to produce red blood cells and keep you in good health. In your body, iron becomes a part of your hemoglobin and myoglobin. Hemoglobin carries oxygen through your blood to tissues and organs. Myoglobin helps your muscle cells store oxygen.