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Ferrous Sulfate

Evidence Level
Very Strong
2 Clinical Trials
5 Documented Benefits
5/5 Evidence Score

Ferrous sulfate is the most common, cheapest, and longest-established oral iron form — recommended by WHO as standard treatment for iron deficiency anemia. ~20% elemental iron by weight. Effective for raising hemoglobin but causes substantial GI side effects (constipation, nausea, dark stools, metallic taste) — 40-50% of patients quit due to intolerance. Considered the gold-standard comparator in iron bioavailability research.

Studied Dose 60-200 mg elemental iron/day for adult IDA treatment (often 325 mg ferrous sulfate = 65 mg elemental Fe, taken 1-3× daily)
Active Compound Ferrous sulfate (FeSO4)

Benefits

Established Standard for Iron Deficiency

Ferrous sulfate is WHO-recommended first-line oral iron for iron deficiency anemia. Decades of clinical use across all populations — pregnant women, children, elderly, post-surgical, post-bleeding. Effective for raising hemoglobin and ferritin.

Supported by Trial 1, Trial 2

High Elemental Iron Content

~20% elemental iron by weight — among the higher-content forms. 325 mg ferrous sulfate provides 65 mg elemental iron. Cost-effective for delivering required iron amounts.

Supported by Trial 2, Trial 1

Lowest Cost Iron Supplement

Ferrous sulfate is the cheapest oral iron form — generic, OTC, and widely available. WHO and developing-world iron supplementation programs rely on ferrous sulfate for affordability and global access.

Supported by Trial 2, Trial 1

Effective in Iron Repletion

Despite GI side effects, ferrous sulfate reliably raises hemoglobin in IDA — meta-analyses show effective response over 8-12 weeks. Slow-release/enteric-coated formulations may improve tolerability while preserving absorption.

Supported by Trial 2, Trial 1

Pediatric Iron Deficiency

Liquid ferrous sulfate (drops, syrup) is widely used for pediatric iron deficiency — though staining of teeth is a concern with prolonged use; offered with straw and rinsing recommendations.

Supported by Trial 1, Trial 2

Mechanism of action

1

Ferrous (Fe²⁺) Form

Iron exists in two oxidation states: ferrous (Fe²⁺) and ferric (Fe³⁺). The body absorbs ferrous iron preferentially via DMT1 transporter in duodenal enterocytes. Ferric iron must be reduced before absorption — ferrous forms (sulfate, fumarate, gluconate) bypass this step.

2

DMT1 Transport

Divalent metal transporter 1 (DMT1) on duodenal enterocyte apical membrane absorbs Fe²⁺. Once inside, iron is exported via ferroportin to plasma transferrin for delivery to bone marrow (erythropoiesis), liver storage (ferritin), and other tissues.

3

Hepcidin Regulation

Hepcidin (liver-derived hormone) regulates iron absorption — high iron status raises hepcidin, blocking ferroportin and reducing absorption. Inflammation also raises hepcidin (functional iron deficiency in chronic disease).

4

Stomach Acid Dependence

Ferrous sulfate absorption is enhanced by gastric acid (low pH). PPIs and atrophic gastritis reduce iron absorption. Vitamin C improves absorption by reducing Fe³⁺ to Fe²⁺ and forming soluble complexes.

Clinical trials

1
Ferrous Sulfate vs Ferric Polymaltose for IDA — Clinical Overview

Clinical reviews comparing ferrous sulfate vs ferric polymaltose for iron deficiency anemia treatment.

Pooled across IDA clinical trials.

Ferrous sulfate produces 3-4× greater hemoglobin response than ferric polymaltose preparations. Established as standard treatment. Slow-release ferrous sulfate maintains efficacy with somewhat improved tolerability.

2
Ferrous Sulfate Tolerability — Evidence Review

Evidence review examining tolerability of various oral iron supplements vs placebo. (PLoS ONE)

Pooled across iron supplement clinical trials.

Ferrous sulfate had significantly higher rates of GI adverse events vs placebo: constipation, nausea, abdominal pain, metallic taste. Adherence is the major clinical limitation — 40-50% of patients reduce dose or discontinue due to side effects. Alternative forms (bisglycinate, fumarate, slow-release) may improve tolerability.

Side effects and drug interactions

Common Potential side effects

CONSTIPATION — most common; affects 30-50% of users.
NAUSEA, gastric discomfort.
Dark/black stools — expected, harmless, but can mask GI bleeding.
Metallic taste.
Tooth staining with liquid forms — use straw, rinse mouth.
Diarrhea (less common; some patients experience this instead of constipation).
PEDIATRIC IRON POISONING — accidental ingestion is a leading cause of pediatric poisoning death; iron supplements MUST be kept out of reach of children; iron-containing products require child-resistant packaging.

Important Drug interactions

Tetracycline/quinolone antibiotics — chelation; separate by 2 hours.
Levothyroxine — reduces absorption; separate by 4 hours.
Bisphosphonates — separate by 2 hours.
Methyldopa, levodopa — iron reduces absorption.
Mycophenolate — reduces absorption.
Calcium — competes for absorption; separate dosing.
Antacids/PPIs/H2 blockers — reduce iron absorption (gastric acid needed); take iron between PPI doses if possible.
Coffee/tea (tannins) — reduce iron absorption; separate by 1-2 hours.
Vitamin C — ENHANCES absorption (take together for better effect).
Vitamin E — high doses may reduce iron absorption.

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Frequently asked questions about Ferrous Sulfate

What is ferrous sulfate used for?

Ferrous sulfate is the most common and economical iron supplement, used to correct or prevent iron-deficiency anemia. It provides a well-absorbed form of iron, though it is also the form most likely to cause stomach side effects.

How much ferrous sulfate should I take?

A standard 325 mg ferrous sulfate tablet provides about 65 mg of elemental iron. Many people need less, and every-other-day dosing is increasingly recommended. Only take iron to treat a confirmed deficiency, under medical guidance.

Why does ferrous sulfate upset my stomach?

Ferrous sulfate commonly causes constipation, nausea, and cramping. Taking it with a little food, lowering the dose, dosing every other day, or switching to a gentler form like ferrous bisglycinate can help. Dark stools are normal and harmless.

How can I absorb ferrous sulfate better?

Take it with vitamin C (such as orange juice) and away from coffee, tea, dairy, and calcium, which block absorption. Taking it on an empty stomach maximizes absorption but increases stomach upset, so balance the two.

What is Ferrous Sulfate?

Ferrous sulfate is the most common, cheapest, and longest-established oral iron form — recommended by WHO as standard treatment for iron deficiency anemia. ~20% elemental iron by weight.

References(4 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Stoffel NU, Cercamondi CI, Brittenham G, Zeder C, Geurts-Moespot AJ, Swinkels DW, Moretti D, Zimmermann MB. 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. Lancet Haematol. 2017;4(11):e524-e533. doi: 10.1016/S2352-3026(17)30182-5.PubMedUsed to support: Two RCTs showing daily and twice-daily iron dosing raise serum hepcidin and lower fractional absorption from later doses; alternate-day single morning doses optimize cumulative absorption — the basis for alternate-day oral iron regimens.
  2. Moretti D, Goede JS, Zeder C, Jiskra M, Chatzinakou V, Tjalsma H, Melse-Boonstra A, Brittenham G, Swinkels DW, Zimmermann MB. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood. 2015;126(17):1981-9. doi: 10.1182/blood-2015-05-642223.PubMedUsed to support: Stable-isotope study: single iron doses >=60 mg elevate hepcidin for up to 24 h and suppress next-day absorption; fractional absorption falls as dose rises. Supports lower doses (40-80 mg) and avoiding twice-daily dosing — the hepcidin mechanism.
  3. Tolkien Z, Stecher L, Mander AP, Pereira DI, Powell JJ. Ferrous sulfate supplementation causes significant gastrointestinal side-effects in adults: a systematic review and meta-analysis. PLoS One. 2015;10(2):e0117383. doi: 10.1371/journal.pone.0117383.PubMedUsed to support: Meta-analysis (43 trials, 6,831 adults): ferrous sulfate roughly doubles GI side-effects versus placebo (OR 2.32) and versus IV iron (OR 3.05), with no clear dose relationship — quantifying the tolerability problem that limits adherence to oral iron.
  4. Lopez A, Cacoub P, Macdougall IC, Peyrin-Biroulet L. Iron deficiency anaemia. Lancet. 2016;387(10021):907-16. doi: 10.1016/S0140-6736(15)60865-0.PubMedUsed to support: Authoritative seminar on iron-deficiency anaemia: positions oral ferrous salts (ferrous sulfate) as inexpensive first-line therapy for correcting IDA, while reviewing absorption, tolerability limits, and when to escalate to intravenous iron.