Drug Interaction Report

Cholestyramine and Calcifediol: Interaction Details

Name: Cholestyramine and Calcifediol Interaction
Creator: Dr. Brian Staiger, PharmD, BCPS

A pharmacist-reviewed analysis of the Cholestyramine and Calcifediol interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Cholestyramine

Prevalite Questran

Calcifediol

Rayaldee Rayaldee®

Medically reviewed by

Dr. Brian Staiger, PharmD, BCPS

Updated Aug 8, 2026

Editorial policy · Data sources

Interaction severity

Moderate

Can be significant — usually manageable with monitoring.

Minor

Moderate

Major

Contraindicated

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.

Of 40 documented Cholestyramine interactions, 23 are rated moderate — including this one.

Onset

unspecified

Evidence

theoretical

Severity

Moderate

What happens

Decreased absorption of calcifediol

Interaction Deep Dive

Concomitant use of calcifediol and cholestyramine may result in reduced calcifediol absorption. Monitor serum calcium, intact parathyroid hormone, and 25-hydroxyvitamin D concentrations when a patient starts or stops cholestyramine. Adjust the dose of calcifediol if necessary¹.

Why it happens (mechanism)

Unknown

Common questions

Can I take Cholestyramine and Calcifediol together?

Decreased absorption of calcifediol Always confirm with your pharmacist or prescriber before making any change.

How serious is the Cholestyramine and Calcifediol interaction?

It is rated moderate. Can be significant — usually manageable with monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

Questions for your pharmacist

Does my dose of Cholestyramine or Calcifediol 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)

Product Information: RAYALDEE(R) oral extended-release capsules, calcifediol oral extended-release capsules. OPKO Pharmaceuticals LLC (per FDA), Miami, FL, 2016. DailyMed

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Cholestyramine

Keep reading about Cholestyramine

All Cholestyramine interactions (40)

Also serious with: Deferasirox Dexamethasone Injection Dexamethasone Ophthalmic Digoxin

Calcifediol

Keep reading about Calcifediol

All Calcifediol interactions (63) Calcifediol drug information

Also serious with: Burosumab-Twza Injection Burosumab-Twza Midazolam Injection Brivaracetam Injection

Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Cholestyramine + Activated Charcoal Coffee Charcoal European Mandrake Glucomannan Guar Gum Gum Arabic Niacin Slippery Elm + 11 more

Calcifediol + Activated Charcoal Grapefruit St. John's Wort Acacia Rigidula Adrafinil African Wild Potato American Elder Astaxanthin + 130 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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A message from HelloPharmacist

About our interaction database: depth, not breadth

HelloPharmacist doesn't license one of the big commercial interaction databases, so what you'll find here is not a complete list of every known drug interaction. Instead, each entry is researched, analyzed, and written up individually — documented from the published literature, reviewed by a pharmacist, and cited so you can check every source yourself.

If a combination isn't listed here, it means we haven't documented it yet — never that it's safe. For screening a full medication list, we recommend pairing this site with a comprehensive tool like the Drugs.com Interaction Checker and, most importantly, a review by your own pharmacist. For a deep, plain-English, fully sourced explanation of a specific documented interaction — that's exactly what we built this for.

This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.