What is the recommended dose of ferrous sulfate (iron supplement) for treating iron deficiency anemia?

Ferrous Sulfate Dosing for Iron Deficiency Anemia

The recommended dose of ferrous sulfate for treating iron deficiency anemia in adults is 200 mg three times daily (600 mg total daily), which provides approximately 180-200 mg of elemental iron per day, and treatment should continue for 3 months after hemoglobin normalizes to replenish iron stores. 1

Standard Adult Dosing

• Ferrous sulfate 200 mg three times daily is the most cost-effective first-line treatment for iron deficiency anemia in adults 1
• This regimen provides approximately 60-65 mg of elemental iron per 200 mg tablet, totaling 180-195 mg elemental iron daily 2
• Ferrous gluconate and ferrous fumarate are equally effective alternatives when equivalent elemental iron doses are given 1
• A simplified regimen of one tablet daily or alternate-day dosing may be equally effective and better tolerated, though this represents a lower dose approach 1, 2

Optimized Dosing Strategy

The most recent British Society of Gastroenterology guidelines (2021) recommend a more conservative initial approach:

• Start with one tablet per day of ferrous sulfate, fumarate, or gluconate 1
• If not tolerated, reduce to one tablet every other day, which may be as effective with fewer side effects 1, 2
• This lower-dose strategy balances efficacy with tolerability, as gastrointestinal side effects are dose-dependent 1, 3

Administration for Maximum Absorption

• Take on an empty stomach (1 hour before or 2 hours after meals) for optimal absorption 2, 3
• Food reduces iron absorption by 40-50% 3
• Add ascorbic acid 250-500 mg twice daily if response is poor, as vitamin C enhances iron absorption 1, 2
• Avoid concurrent calcium supplements, dairy products, tea, coffee, or antacids, which impair absorption 3

Duration and Monitoring

• Continue treatment for 3 months after hemoglobin normalizes to adequately replenish bone marrow iron stores 1, 3
• Expect hemoglobin to rise by approximately 2 g/dL after 3-4 weeks of treatment 1, 2
• Monitor hemoglobin response at 4 weeks; failure to respond suggests poor compliance, continued blood loss, malabsorption, or misdiagnosis 1, 2, 3
• After normalization, monitor hemoglobin and red cell indices every 3 months for one year, then annually 1, 3

Special Populations

Pregnant Women

• 60-120 mg elemental iron daily (approximately 200-400 mg ferrous sulfate) 3, 4
• Iron deficiency affects up to 84% of pregnant women in the third trimester 4

Pediatric Patients

• 2-3 mg/kg/day of elemental iron for children with iron deficiency anemia 2, 5
• A single daily dose is as effective as three-times-daily dosing and may improve adherence 6
• For young children (6-53 months), 2 mg/kg/day of ferrous sulfate oral solution normalizes hemoglobin in 95% of cases within 3 months 7
• Low-dose ferrous sulfate (3 mg/kg once daily) is superior to iron polysaccharide complex for increasing hemoglobin in children aged 9-48 months 8

Women with Heavy Menstrual Bleeding

• May require 50-100 mg elemental iron daily (approximately 150-300 mg ferrous sulfate) 3

Inflammatory Bowel Disease

• Do not exceed 100 mg elemental iron per day (approximately 300 mg ferrous sulfate), as higher doses may worsen inflammation 3

When to Switch to Intravenous Iron

Consider parenteral iron when:

• Intolerance to at least two different oral iron preparations 1, 2
• Malabsorption conditions (celiac disease, inflammatory bowel disease, post-bariatric surgery) 2, 4
• Inadequate response after 3-4 weeks of appropriate oral therapy despite compliance 2, 3
• Ongoing blood loss exceeding oral iron absorption capacity 2
• Chronic inflammatory conditions (chronic kidney disease, heart failure, cancer) 1, 2, 4
• Second and third trimesters of pregnancy when rapid repletion is needed 4

Common Pitfalls to Avoid

• Don't assume all iron preparations are equivalent: ferrous sulfate provides more elemental iron per tablet (60-65 mg) than ferrous gluconate (35-38 mg), making it more cost-effective 2
• Don't defer iron replacement while awaiting investigations unless colonoscopy is imminent 1
• Don't continue indefinitely without monitoring: failure to respond indicates continued blood loss, malabsorption, misdiagnosis, or non-compliance 1, 2
• Don't overlook the underlying cause: identifying and treating the source of iron loss is essential 1
• Don't prescribe parenteral iron as first-line: it is painful (intramuscular), expensive, carries anaphylaxis risk, and provides no faster hemoglobin rise than oral preparations 1