Strong evidenceVitamins & minerals

Ferrous Sulfate

The reference treatment for iron-deficiency anemia: cheap, effective and extensively studied. The remaining questions are about dosing schedule and tolerability, not about whether it works.

Evidence last reviewed: August 2026

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What the science says

Corrects iron-deficiency anemia Strong evidence
In a randomized trial in 208 anemic infants, 84 days of ferrous sulfate cut anemia prevalence from 83.7% to 46.2% and raised haemoglobin and ferritin, matching heme iron on both primary endpoints. A separate randomized comparison of four oral iron salts in 120 pregnant women found all effective at normalising haemoglobin.
Alternate-day dosing absorbs better Moderate evidence
Two randomized isotope studies in iron-depleted women found alternate-day dosing raised cumulative fractional absorption to 21.8% versus 16.3% on consecutive days, and that splitting a daily dose in two increased hepcidin and reduced absorption compared with one morning dose.

Dosage & safety

Studied doseFor treating anemia, 100–200 mg elemental iron/day (325 mg ferrous sulfate ≈ 65 mg elemental iron), best as a single morning dose or on alternate days. Vitamin C or orange juice improves absorption; tea, coffee, dairy and calcium reduce it. Recheck blood counts after 2–4 weeks and continue for 3 months after haemoglobin normalises to refill stores.

SafetyConstipation, nausea, dark stools and epigastric pain are common and dose-related — alternate-day dosing often helps. Accidental overdose is life-threatening in children; store sealed and out of reach. Avoid in haemochromatosis and in anemia not proven to be iron deficiency, since supplementing masks the cause. Separate by several hours from levothyroxine, tetracyclines, quinolones and antacids.

Scientific references

Heme iron compared with ferrous iron salts to treat iron deficiency anemia in Gambian children: a randomized controlled trial
Bah M, Verhoef H, Okoh E — Am J Clin Nutr, 2025
A randomized controlled trial comparing the efficacy, tolerability, and cost of oral iron preparations in iron-deficiency anemia in pregnancy
Gamad N, Saha PK, Sharma P — J Obstet Gynaecol Res, 2021
Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials
Stoffel NU, Cercamondi CI, Brittenham G — Lancet Haematol, 2017

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