Mercaptopurine and Azathioprine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Azathioprine
Mercaptopurine
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
Myelosuppression, impaired renal function, and hepatotoxicity
Interaction Deep Dive
Mercaptopurine is an active metabolite of azathioprine1. Profound myelosuppression, severe sepsis and subsequent death has been reported in a patient who took azathioprine 150 mg once a day with mercaptopurine 100 mg daily 2. It is clinically unnecessary and inadvisable to use these two medications simultaneously.
Why it happens (mechanism)
Additive adverse effects
Common questions
Can I take Mercaptopurine and Azathioprine together?
Myelosuppression, impaired renal function, and hepatotoxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Mercaptopurine and Azathioprine interaction?
It is rated major. Potentially serious — often needs a change or close 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 Mercaptopurine or Azathioprine 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 a safer alternative to one of these medications for me?
References (2)
- Product Information: IMURAN(R) oral tablets, IV injection, azathioprine oral tablets, IV injection. Prometheus Laboratories, San Diego, CA, 2005. DailyMed
- None Listed: Duplication with azathioprine and mercaptopurine. ISMP Acute Care Med Saf Alert 2006; 11(13):3-4.
Keep reading about Azathioprine
Keep reading about Mercaptopurine
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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