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Ferrous Sulfate: Uses, How It Works, and Safety Information

Last reviewed: December 2025

Overview

Ferrous sulfate is an iron supplement used to treat or prevent iron deficiency anemia. It’s one of the most commonly prescribed and recommended forms of iron supplementation, available both over-the-counter and by prescription.

Iron is essential for producing hemoglobin, the protein in red blood cells that carries oxygen throughout your body. When iron levels are low, the body cannot make enough healthy red blood cells, leading to fatigue, weakness, and other symptoms of anemia.

Brand Names

  • Feosol
  • Fer-In-Sol
  • Slow FE
  • Feratab
  • Various generic and store brands

How It Works

Ferrous sulfate provides elemental iron in its ferrous (Fe²⁺) form, which is more readily absorbed by the body than ferric (Fe³⁺) iron. Once absorbed in the small intestine, iron is:

  • Transported to bone marrow for hemoglobin production
  • Stored in the liver, spleen, and bone marrow as ferritin
  • Used for various enzymatic functions throughout the body

The sulfate salt dissolves readily in the stomach, releasing iron for absorption primarily in the duodenum and upper jejunum.

Common Uses

Iron deficiency anemia:

  • Most common indication
  • Restores hemoglobin levels
  • Replenishes iron stores

Prevention of iron deficiency:

  • During pregnancy
  • Heavy menstrual periods
  • Blood donation recovery
  • Vegetarian or vegan diets

Other conditions causing iron loss:

  • Chronic blood loss (GI conditions)
  • Post-surgical recovery
  • Malabsorption syndromes (with medical supervision)

Forms Available

Immediate-release tablets:

  • 325 mg tablets (65 mg elemental iron)
  • Most common form
  • Take on empty stomach for best absorption

Extended-release formulations:

  • Slow FE and similar products
  • May reduce GI side effects
  • Slightly lower absorption

Liquid forms:

  • Fer-In-Sol drops for infants
  • Elixirs for those who can’t swallow tablets
  • Often causes tooth staining

Important Considerations

Absorption factors:

  • Vitamin C enhances absorption (take with orange juice)
  • Calcium, antacids, and dairy reduce absorption
  • Take 2 hours apart from other medications
  • Empty stomach improves absorption but increases side effects

Who should avoid or use caution:

  • Hemochromatosis (iron overload disorder)
  • Repeated blood transfusions
  • Hemolytic anemias
  • Thalassemia (without iron deficiency)

Duration of treatment:

  • Typically 3-6 months to replenish stores
  • Hemoglobin improves within 2-4 weeks
  • Continue 2-3 months after levels normalize

Sources

  • FDA-approved labeling for ferrous sulfate products
  • American Society of Hematology guidelines
  • National Institutes of Health Office of Dietary Supplements
  • Manufacturer prescribing information
Last reviewed: December 2025