Iron and Cholestyramine Resin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Cholestyramine Resin
Iron
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Decreased iron effectiveness
Interaction Deep Dive
Concomitant cholestyramine and iron administration may result in the binding of iron in the GI tract preventing its absorption. Although the significance of this interaction is not established, it appears that cholestyramine may impair the absorption of dietary iron1.
Why it happens (mechanism)
Cholestyramine binds iron
Common questions
Can I take Iron and Cholestyramine Resin together?
Decreased iron effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Iron and Cholestyramine Resin interaction?
It is rated minor. Usually limited clinical impact.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Iron or Cholestyramine Resin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (1)
- Thomas FB, McCullough FS, & Greenberger NJ: Inhibition of the intestinal absorption of inorganic and hemoglobin iron by cholestyramine. J Lab Clin Med 1971; 78:70-80.
Keep reading about Cholestyramine Resin
Keep reading about Iron
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