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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.

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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.

How to take it

TimingOne morning dose, or alternate days — splitting it through the day raises hepcidin and absorbs less overall.
With food?On an empty stomach for best absorption, with a little food only if nausea would otherwise make you stop.
Worth knowingRecheck blood counts at 2–4 weeks, and keep going for three months after haemoglobin normalises to actually refill stores.

Interactions

With medications

  • levothyroxine

    Iron binds it in the gut and reduces absorption substantially. separate by at least 4 hours

  • tetracycline and quinolone antibiotics

    Mutual chelation reduces absorption of both. separate by at least 2–4 hours

  • proton-pump inhibitors and antacids

    Less stomach acid means less iron absorbed. take iron with vitamin C and as far from the antacid dose as possible

  • levodopa and methyldopa

    Iron chelates them and lowers their effect. separate by at least 2 hours

With other supplements

  • calcium

    Calcium competes with iron for absorption. take them at different times of day

  • vitamin C

    Vitamin C substantially increases non-heme iron absorption. take them together deliberately

  • zinc

    High doses compete for the same absorption pathways. separate by at least 2 hours

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does ferrous sulfate work for iron deficiency anemia?

Yes: ferrous sulfate is the reference treatment, with strong evidence. In a trial of 208 anaemic infants, 84 days of ferrous sulfate cut anaemia prevalence from 83.7% to 46.2%.

Is taking iron every other day better?

Alternate-day dosing absorbs better: randomized isotope studies in iron-depleted women found 21.8% fractional absorption on alternate days versus 16.3% on consecutive days, a moderate-grade finding. Splitting a daily dose in two raised hepcidin and reduced absorption compared with one morning dose.

How much ferrous sulfate should I take?

For anaemia, the usual dose is 100–200 mg of elemental iron a day; a 325 mg ferrous sulfate tablet gives about 65 mg. Recheck blood counts at 2–4 weeks and continue for 3 months after haemoglobin normalises to refill stores.

What should I not take with ferrous sulfate?

Tea, coffee, dairy and calcium reduce ferrous sulfate absorption, while vitamin C improves it. Separate iron by at least 4 hours from levothyroxine and by 2–4 hours from tetracycline and quinolone antibiotics.

Scientific references

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