Slow Fe has a controlled delivery system that helps provide high potency iron while being gentle on your stomach, so you experience fewer GI side effect (nausea and abdominal discomfort) common to iron use. Slow Fe is an iron supplement for iron deficiency and iron deficiency anemia when the need for such therapy has been determined by a physician. The 45 mg of elemental iron in each tablet is equivalent to 142 mg of ferrous sulfate.