Hematinics · Hematology
Ferrous sulfate
iron sulfate · oral iron · Feosol® · Ferro-Grad®(brand names vary by market)
Cheap, effective, badly tolerated, and best given every other day.
Also: oral liquid, modified release
Mechanism
Provides elemental iron for haem synthesis. Absorption is tightly regulated by hepcidin, which rises for about a day after each dose and blocks the next one.
Indications
- Iron deficiency anemia
- Iron deficiency without anemia
- Pregnancy supplementation
Formulations
Dosing concepts
Alternate-day dosing
A dose raises hepcidin for roughly 24 hours, so a second dose the next morning is largely blocked. Alternate-day dosing absorbs more total iron with fewer side effects, which is counter-intuitive and well evidenced.
Duration
Continued for about three months after the hemoglobin normalises, to refill stores rather than just the blood.
Absorption
Taken away from food, tea, calcium and proton pump inhibitors; vitamin C improves uptake.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~10 to 15%, and much lower with food or in inflammation
- Half-life
- Not applicable; the body has no active excretion route for iron
- Elimination
- plasma: Losses occur only through blood loss and cell shedding, which is why overload is possible
Adverse effects
- Constipationcommon
- Nausea and epigastric discomfortcommonDose-related; alternate-day dosing helps considerably.
- Black stoolscommonExpected and harmless, but it can mask melena.
- Overdose in childrenseriousIron is a leading cause of fatal childhood poisoning; storage matters.
Contraindications & precautions
Contraindications
- Iron overload states such as hemochromatosis
- Anemia not due to iron deficiency
Precautions
- Undiagnosed anemia, where treating first delays the diagnosis
- Concurrent levothyroxine, doxycycline, quinolones or bisphosphonates
Interactions
Monitoring
Reticulocyte rise at about a week
The earliest proof it is working
Hemoglobin and mean cell volume
Response · 4 to 8 weeks
Ferritin before stopping
To confirm stores are replete, not just the hemoglobin
The cause of the deficiency
In an adult male or postmenopausal female it is a gastrointestinal investigation until proven otherwise
Counselling points
- Take it on an empty stomach if you can tolerate it, with orange juice or a vitamin C tablet.
- Every other day often works better than daily, and upsets the stomach less.
- Keep it four hours away from thyroid tablets, antacids, and some antibiotics.
- Your stools will turn black. That is expected.
- Keep it well out of reach of children: iron tablets are dangerous to them.
Clinical pearls
- Alternate-day dosing is one of the clearest examples of a physiological insight changing practice: more iron is absorbed and fewer patients stop the drug.
- Black stools from iron can mask true melena, so a patient on iron with new symptoms still needs proper assessment rather than reassurance.
References & review
- Ferrous sulfate product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.