Is 200 mg of ferrous sulfate (iron supplement) three times daily too much for a patient with early stage iron deficiency, low ferritin, elevated Total Iron Binding Capacity (TIBC), and low iron saturation, who is concerned about constipation?

Iron Dosing for Early Iron Deficiency Without Anemia

Your proposed dose of ferrous sulfate 200 mg three times daily (195 mg elemental iron/day) is excessive and outdated—current evidence strongly supports once-daily dosing of 50-100 mg elemental iron, which is equally effective with significantly fewer side effects like constipation. 1

Recommended Dosing Strategy

Start with ferrous sulfate 200 mg (65 mg elemental iron) once daily, not three times daily. 1, 2 This approach:

• Provides equal or superior iron absorption compared to multiple daily doses 1
• Dramatically reduces gastrointestinal side effects including constipation 1, 2
• Works because hepcidin (the iron regulatory hormone) remains elevated for 48 hours after iron intake, blocking absorption of subsequent doses 1, 2

Why Three Times Daily Dosing Is Problematic

Multiple daily doses create a physiologic problem:

• The first dose stimulates hepcidin production, which reduces subsequent iron absorption by 35-45% 1
• Overall iron absorption from 60 mg once daily equals that from 60 mg twice daily 1
• Three times daily dosing increases constipation and other GI side effects without improving efficacy 1, 2

Optimizing Your Single Daily Dose

To maximize absorption and minimize constipation:

• Take ferrous sulfate 200 mg once daily on an empty stomach 1, 2
• Add vitamin C 500 mg with the iron dose to enhance absorption 1, 2
• If constipation still occurs, switch to alternate-day dosing (every other day), which actually increases fractional iron absorption while improving tolerance 1
• Avoid taking with coffee, tea, calcium, or antacids as you correctly noted 1

Alternative if Side Effects Persist

If ferrous sulfate causes intolerable constipation even at once-daily dosing:

• Try ferrous fumarate or ferrous gluconate at equivalent elemental iron doses 1, 2
• Consider ferric maltol 30 mg twice daily, which has comparable GI side effects to placebo but is more expensive 1
• All oral iron formulations have equal efficacy—the choice is purely based on tolerability and cost 2

Expected Response and Monitoring

With once-daily dosing:

• Recheck labs at 3-4 weeks (not 3-4 weeks as you mentioned, though your timing is appropriate) 1, 2
• Expect ferritin to rise and iron saturation to improve 1
• Continue for 3 months after levels normalize to fully replenish iron stores 1, 2
• Monitor periodically every 6 months initially 1

Your Diagnostic Workup Is Appropriate

Your plan to evaluate causes is correct:

• Assess menstrual blood loss first in premenopausal women (accounts for 5-10% of iron deficiency) 2
• Screen for celiac disease with antiendomysial antibody and IgA measurement 2
• Evaluate dietary intake and NSAID use 1
• Consider GI investigation only if alarm symptoms present 2

Critical Pitfall to Avoid

Do not prescribe 200 mg three times daily (600 mg total, 195 mg elemental iron)—this outdated regimen guarantees constipation and other GI side effects without improving outcomes. 1, 2 The traditional three-times-daily dosing is based on a single small, poor-quality study and contradicts current physiologic understanding of iron absorption 3.

When to Consider IV Iron

Switch to intravenous iron only if:

• Intolerance to at least two different oral iron preparations 1, 2
• No improvement in ferritin after 4 weeks of compliant oral therapy 2
• Malabsorption conditions (active IBD, celiac disease with ongoing gluten exposure, post-bariatric surgery) 1, 2

Bottom line: Start with ferrous sulfate 200 mg once daily with vitamin C 500 mg. This provides adequate elemental iron (65 mg) to correct your deficiency while minimizing constipation risk. 1, 2