Ferrous fumarate and ferrous sulfate are both iron-based supplements with slightly differing chemical formulas. They are both commonly taken as dietary supplements for those with iron deficiencies.
Ferrous sulfate and ferrous fumarate both provide iron in the form of tablets. The iron the tablets contain is called elemental iron and is taken to relieve deficiencies of iron in the body. Ferrous fumarate contains more iron per 325 milligram tablet than ferrous sulfate.
Iron deficiency can be caused by an inadequate amount of iron in the diet or by a health problem called anemia. Anemia is a condition in which blood cells lack the proper nutrients to carry sufficient oxygen throughout the body.