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Best form of oral iron

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"Iron Deficiency Anemia"[MeSH Terms] AND oral iron

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oral iron supplementation formulations ferrous sulfate alternate day guideline iron deficiency anemia

For most adults with iron deficiency, ferrous sulfate is the best first-choice oral iron: effective, widely available, and inexpensive. No oral formulation has shown a clear overall advantage over others. The American Gastroenterological Association specifically prefers ferrous sulfate on cost grounds (AGA guidance).
Practical regimen
  • Ferrous sulfate 325 mg contains about 65 mg elemental iron.
  • Take one tablet once daily, or every other day if nausea, constipation, or abdominal discomfort occurs.
  • Alternate-day dosing is often better tolerated and can provide comparable absorption/response (2024 systematic review).
Alternatives if sulfate is not tolerated
  • Ferrous gluconate: less elemental iron per tablet, sometimes gentler on the stomach.
  • Ferrous fumarate: more elemental iron per tablet.
  • These are reasonable substitutes, but are not inherently “better” than sulfate.
How to take it
  • Best absorbed away from food, but take with a small snack if side effects prevent adherence.
  • Avoid taking it at the same time as calcium supplements, antacids, tea, coffee, or dairy.
  • Avoid enteric-coated or sustained-release iron when possible because absorption may be poorer. Textbook of Family Medicine, 9e, Key Points section.
  • Dark stools and constipation are common and usually harmless.
If hemoglobin or ferritin does not improve after a trial, or if there is malabsorption, ongoing heavy blood loss, inflammatory bowel disease, advanced kidney disease, or intolerance, the issue may be the diagnosis/cause or a need for IV iron rather than a different oral product.
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