Managing Constipation from Iron Tablets
The most effective strategy is to switch to once-daily or alternate-day dosing (every other day) of iron, which reduces gastrointestinal side effects including constipation while maintaining or even improving iron absorption. 1
Optimal Dosing Strategy to Minimize Constipation
Take iron once daily rather than multiple times per day, as increased dosing frequency elevates hepcidin for 24 hours, which not only reduces absorption of subsequent doses by 35-45% but also increases side effects including constipation 1
Consider switching to alternate-day (every-other-day) dosing if daily dosing causes intolerable constipation, as this significantly increases fractional iron absorption while reducing gastrointestinal symptoms 1
Start with or reduce to 50-100 mg of elemental iron (equivalent to one 200 mg ferrous sulfate tablet containing 65 mg elemental iron), as lower doses cause fewer side effects 1
Timing and Administration Adjustments
Take iron in the morning on an empty stomach when possible, as serum hepcidin increases during the day and morning dosing provides superior absorption 1
If constipation is severe, consider taking iron with small amounts of food or at bedtime to improve tolerability, though this reduces absorption by up to 50% 2
Add 500 mg of vitamin C when taking iron to enhance absorption, especially if taking with meals, which can partially offset the reduced absorption from food 1, 2
Alternative Iron Formulations
Try switching to a different ferrous salt formulation (ferrous gluconate or ferrous fumarate instead of ferrous sulfate) if one formulation causes significant constipation, as individual tolerance varies 1, 3
All standard ferrous iron salts are reasonable first choices with no strong evidence that any formulation is better tolerated than others, but individual response may differ 1, 2
Adjunctive Measures
Increase fluid intake and dietary fiber to counteract iron-induced constipation, though avoid taking iron with fiber-containing foods as fiber reduces iron absorption 2, 4
Stool softeners may be used cautiously if needed, but avoid excessive loosening of stools 5, 4
Avoid taking iron with calcium-containing foods, aluminum-based antacids, or phosphate binders, as these further reduce absorption and may necessitate higher doses that worsen constipation 1, 2
When to Consider Intravenous Iron
Switch to intravenous iron if constipation remains intolerable despite dosing adjustments (alternate-day dosing, lower doses, timing changes) 1
IV iron should also be considered if hemoglobin fails to rise after 2-4 weeks of adherent oral therapy, as this indicates treatment failure 1
Intravenous iron formulations that replace iron deficits with 1-2 infusions (ferric carboxymaltose, low molecular weight iron dextran, ferumoxytol) are preferred 1
Monitoring and Duration
Check hemoglobin at 4 weeks to assess response to therapy 1
Continue treatment for approximately 3 months after hemoglobin normalizes to adequately replenish iron stores, not just correct anemia 1
Do not discontinue therapy prematurely when symptoms improve, as incomplete iron repletion leads to recurrence 1
Critical Pitfalls to Avoid
Never take iron more than once daily unless using alternate-day dosing, as multiple daily doses dramatically increase constipation and other side effects without improving absorption 1, 2
Do not assume all gastrointestinal symptoms including constipation are due to iron—persistent or severe symptoms warrant evaluation for other causes including bowel obstruction, which has been rarely reported with iron pills 3, 5
Avoid consuming iron with tea or coffee within 1-2 hours, as these are powerful inhibitors that may necessitate higher doses and worsen side effects 1