What is the recommended dose of over-the-counter (OTC) iron supplement for a 35-year-old female with anemia?

Recommended OTC Iron Dose for a 35-Year-Old Female with Anemia

For a 35-year-old woman with iron deficiency anemia, take 50-100 mg of elemental iron once daily in the morning on an empty stomach, using ferrous sulfate as the first-line formulation. 1, 2

Specific Dosing Recommendations

First-Line Formulation

• Ferrous sulfate 200 mg tablets (containing 65 mg elemental iron) taken once daily is the most cost-effective option 1, 2
• Alternative formulations if ferrous sulfate is not tolerated include:
  • Ferrous fumarate 210-322 mg tablets (69-106 mg elemental iron) 1, 2
  • Ferrous gluconate 300 mg tablets (37 mg elemental iron) 1, 3

Optimal Timing and Frequency

• Take as a single morning dose rather than divided doses throughout the day 2, 4
• Take on an empty stomach (1-2 hours before or after meals) to maximize absorption 2
• If daily dosing causes intolerable side effects, switch to alternate-day dosing (every other day) with 100-120 mg elemental iron, which actually increases fractional iron absorption 2, 4, 5

Strategies to Enhance Absorption and Reduce Side Effects

To Improve Absorption

• Take with 250-500 mg vitamin C (ascorbic acid) to enhance iron absorption 1, 2
• Avoid taking iron with tea, coffee, or calcium-containing foods/supplements, which inhibit absorption 2

To Minimize Side Effects

• If gastrointestinal side effects occur (nausea, constipation), consider:
  • Taking with food (though this reduces absorption) 2
  • Switching to alternate-day dosing 4, 5
  • Trying a different iron formulation 1, 2

Duration of Treatment

• Continue treatment for approximately 3 months after hemoglobin normalizes to adequately replenish iron stores 2, 6, 7
• Total treatment duration is typically 3-12 weeks depending on severity 7

Monitoring Response

• Expect hemoglobin to increase by at least 10 g/L (1 g/dL) within 2 weeks if treatment is effective 1, 2
• If hemoglobin does not rise by at least 10 g/L after 2 weeks of daily oral iron, this strongly predicts treatment failure (sensitivity 90.1%, specificity 79.3%) 1
• Monitor hemoglobin response within the first 4 weeks of treatment 2

Common Pitfalls to Avoid

• Do not take multiple doses per day (e.g., 2-3 times daily as suggested on some FDA labels 3, 8) - this increases side effects without improving absorption due to hepcidin elevation that persists 24 hours after each dose 4, 5
• Avoid modified-release preparations - these are considered "less suitable for prescribing" according to the British National Formulary 1, 2
• Do not rely on multivitamins as they contain insufficient elemental iron (typically ≤14 mg) for treating anemia 1, 2

When to Consider Alternative Approaches

• Consider intravenous iron if: 2, 7
  • Oral iron is not tolerated despite modifications
  • No improvement in ferritin levels after an adequate oral iron trial
  • Conditions impairing oral iron absorption are present (inflammatory bowel disease, post-bariatric surgery)
  • Rapid correction of anemia is needed (e.g., prior to surgery)

Special Consideration for Alternate-Day Dosing

• Recent high-quality evidence shows that alternate-day dosing with 100-120 mg elemental iron may be superior to daily dosing because: 4, 5
  • Oral iron doses ≥60 mg stimulate hepcidin elevation that persists 24 hours, blocking absorption of subsequent doses
  • Fractional iron absorption is significantly higher with alternate-day dosing (21.8% vs 16.3%, p=0.0013)
  • Total iron absorption over 14 days is also higher (175.3 mg vs 131.0 mg, p=0.0010)
  • Side effects are reduced compared to daily dosing