What the FDA labels say about taking them together
Allopurinol and mercaptopurine
Allopurinol's FDA label of May 21, 2026 names mercaptopurine in its drug interactions section, and mercaptopurine's label names allopurinol too. The mercaptopurine label: “DRUG INTERACTIONS Allopurinol: Reduce the dose of MERCAPTOPURINE when co-administered with allopurinol.”
Check it at the source: the allopurinol FDA label on DailyMed (effective May 21, 2026, Rising Pharma Holdings, Inc.); the mercaptopurine FDA label on DailyMed (effective July 20, 2026, Nova Laboratories, Ltd).
What does the allopurinol label say about mercaptopurine?
Allopurinol label, drug interactionsAvoid concomitant use. ( 7.2 ) Mercaptopurine or Azathioprine: Reduce mercaptopurine or azathioprine dose as recommended in the respective prescribing information.
Allopurinol label, warnings and precautionsConcomitant use with allopurinol increases the exposure of either mercaptopurine or azathioprine which may increase the risk of myelosuppression.
Allopurinol label (Proficient Rx LP, February 1, 2023), drug interactionsDrug Interactions In patients receiving mercaptopurine or azathioprine, the concomitant administration of 300-600 mg of allopurinol per day will require a reduction in dose to approximately one-third to one-fourth of the usual dose of mercaptopurine or azathioprine.
Source: FDA drug label (Aloprim, NDA020298), Mylan Institutional LLC, effective February 18, 2022 (SPL set 10cc918f-aa44-415b-932d-2404695ac449), via openFDA
Source: FDA drug label (Allopurinol, NDA018877), Proficient Rx LP, effective February 1, 2023 (SPL set 0ca4baed-c5d8-4de4-ac17-6e5d1df15c03), via openFDA
Source: FDA drug label (Allopurinol), Rising Pharma Holdings, Inc., effective May 21, 2026 (SPL set 30ad5ba2-1cef-4933-b104-0597f6a2aaa2), via openFDA; the full label on DailyMed
What does the mercaptopurine label say about allopurinol?
Mercaptopurine label, drug interactionsDRUG INTERACTIONS Allopurinol: Reduce the dose of MERCAPTOPURINE when co-administered with allopurinol.
Mercaptopurine label (Florida Pharmaceutical Products, LLC, January 30, 2026), warnings and precautionsMyelosuppression can be exacerbated by coadministration with allopurinol, aminosalicylates or other products that cause myelosuppression [see Drug Interactions (7.1, 7.3, 7.4)].
Source: FDA drug label (Mercaptopurine, NDA009053), Florida Pharmaceutical Products, LLC, effective January 30, 2026 (SPL set e7309808-5ae8-4a55-90e3-3992ace0da62), via openFDA
Source: FDA drug label (MERCAPTOPURINE), Nova Laboratories, Ltd, effective July 20, 2026 (SPL set 9c6fc66b-522f-499d-961a-cde6ca0ec2e5), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Allopurinol | Mercaptopurine | |
|---|---|---|
| Labeled for | Gout | Leukemia, lymphoma and myeloma |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $0.0315 per tablet 100 mg tablet | $1.07 per tablet 50 mg tablet |
| Shortage now | A presentation being discontinued | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once