Vitamin A and Heparin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Vitamin A
Heparin
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
Increased risk of bleeding
Interaction Deep Dive
Concomitant administration of warfarin and vitamin A can cause an increased anticoagulant effect when large doses of vitamin A are given1. Pretreatment with vitamin A at a dose of 25,000 International Units (IU) daily for 30 days resulted in a moderate increase in the hypoprothrombinemic response of dicumarol in 3 individuals given dicumarol 150 milligrams. Dosage adjustments may be necessary 3.
Why it happens (mechanism)
Unknown
Literature reports
1 report — tap to read
a) Pretreatment with vitamin A at a dose of 25,000 International Units (IU) daily for 30 days resulted in a moderate increase in the hypoprothrombinemic response of dicumarol in 3 individuals given dicumarol 150 milligrams. Dosage adjustments may be necessary 2.
Common questions
Can I take Vitamin A and Heparin together?
Increased risk of bleeding Always confirm with your pharmacist or prescriber before making any change.
How serious is the Vitamin A and Heparin interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
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 "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Vitamin A or Heparin 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 (3)
- Anon: Vitamin supplements. Med Lett Drugs Ther 1985; 27(693):66-68.
- Hansten PDHansten PD: Effects of vitamins on drug action, 1, Drug Interactions Newsletter. Applied Therapeutics, Inc, San Francisco, CA, 1981, pp 35-38.
- Hansten PDHansten PD: Effects of vitamins on drug action, 1, Drug Interactions Newsletter. Applied Therapeutics, Inc, San Francisco, CA, 1981, pp 35-8.
Keep reading about Heparin
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:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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