What is better for treating iron deficiency anemia, ferrous (iron) fumarate or ferrous (iron) sulfate?

Ferrous Sulfate is Preferred Over Ferrous Fumarate

Ferrous sulfate is the recommended first-line oral iron formulation for treating iron deficiency anemia, primarily because it is the least expensive option with equivalent efficacy to other ferrous salts, including ferrous fumarate. 1

Key Recommendation from Guidelines

The 2024 American Gastroenterological Association (AGA) explicitly states: "No single formulation of oral iron has any advantages over any other. Ferrous sulfate is preferred as the least expensive iron formulation." 1

This recommendation is echoed by the 2021 British Society of Gastroenterology guidelines, which recommend "one tablet per day of ferrous sulphate, fumarate or gluconate" without distinguishing efficacy differences between these ferrous salts. 1

Comparative Analysis

Efficacy

• Both ferrous sulfate and ferrous fumarate deliver similar amounts of elemental iron per dose and have comparable absorption rates 1
• Ferrous sulfate 200 mg provides 65 mg elemental iron 1
• Ferrous fumarate 210 mg provides 69 mg elemental iron 1
• No clinical trials demonstrate superior hemoglobin response or iron store repletion with one ferrous salt over another 1

Cost Considerations

• Ferrous sulfate is significantly less expensive: approximately £1.00 per 28 days compared to £1.33 for ferrous fumarate 1
• This cost difference becomes substantial over the typical 3-6 month treatment course required to replenish iron stores 1

Tolerability

• Gastrointestinal side effects are dose-dependent and similar across all ferrous salt formulations 1
• The 2011 UK guidelines note that "other iron compounds (eg, ferrous fumarate, ferrous gluconate) may be tolerated better than ferrous sulphate," but this is not consistently supported by high-quality evidence 1
• If side effects occur with ferrous sulfate, switching to ferrous fumarate is a reasonable option, though reducing dose frequency (alternate-day dosing) may be equally effective 1

Optimal Dosing Strategy

Regardless of which ferrous salt you choose:

• Start with 50-100 mg elemental iron once daily (e.g., one ferrous sulfate 200 mg tablet or one ferrous fumarate 210 mg tablet) 1
• Administer on an empty stomach for optimal absorption 1
• Consider alternate-day dosing if gastrointestinal side effects occur, as this maintains similar iron absorption with better tolerability 1
• Add vitamin C (250-500 mg) to enhance absorption 1

Monitoring Response

• Check hemoglobin after 2-4 weeks: expect at least a 10 g/L (1 g/dL) rise if treatment is effective 1
• Continue treatment for 3 months after hemoglobin normalization to replenish iron stores 1
• If no response occurs, consider switching to intravenous iron rather than trying different oral formulations 1

Clinical Pitfalls to Avoid

• Do not assume ferrous fumarate is "better tolerated" without trial evidence—side effects are primarily dose-related, not formulation-related 1
• Avoid modified-release preparations of either ferrous sulfate or fumarate, as they are less suitable for prescribing due to reduced bioavailability 1
• Do not switch between ferrous salts expecting dramatic improvement—if oral iron fails, the issue is usually absorption, compliance, or ongoing blood loss, not the specific formulation 1

Bottom Line

Choose ferrous sulfate as your default oral iron supplement because it costs less and works just as well as ferrous fumarate. 1 Reserve ferrous fumarate for patients who specifically request an alternative after experiencing side effects with ferrous sulfate, though alternate-day dosing of ferrous sulfate may be equally effective and more cost-efficient. 1