Ferrous Sulfate Tablets are a source of iron, an essential mineral. Iron is used to produce haemoglobin, the oxygen-carrying component of the blood. People with an iron deficency tire easily partly because their bodies are starved for oxygen. Iron is also used to produce myoglobin, which helps muscle cells store oxygen. Without enough iron, adenosine triphosphate (ATP; the fuel the body runs on) cannot be properly synthesized. As a result, some iron-deficient people become fatigued even when their haemoglobin levels are normal (i.e., when they are not anaemic). Iron deficiency is most common in pregnant women, young women during their reproductive years, and children.