What the FDA labels say about taking them together
Mercaptopurine and olsalazine
Mercaptopurine's FDA label (Mercaptopurine) of January 30, 2026 names olsalazine in its drug interactions section, and olsalazine's label names mercaptopurine too. The mercaptopurine label: “Aminosalicylates may inhibit the TPMT enzyme, which may increase the risk of myelosuppression when coadministered with mercaptopurine tablets.”
Check it at the source: the mercaptopurine FDA label on DailyMed (effective July 20, 2026, Nova Laboratories, Ltd); the olsalazine FDA label on DailyMed (effective May 15, 2026, Viatris Specialty LLC).
What does the mercaptopurine label say about olsalazine?
Mercaptopurine label (Florida Pharmaceutical Products, LLC, January 30, 2026), drug interactionsAminosalicylates (e.g., mesalamine, olsalazine or sulfasalazine) may inhibit the TPMT enzyme, which may increase the risk of myelosuppression when coadministered with mercaptopurine tablets.
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
What does the olsalazine label say about mercaptopurine?
Olsalazine label, drug interactionsAzathioprine or 6-Mercaptopurine The concurrent use of mesalamine with azathioprine or 6‑mercaptopurine and/or any other drugs known to cause myelotoxicity (e.g., thioguanine) may increase the risk for blood disorders, bone marrow failure, and associated complications.
Source: FDA drug label (Dipentum), Viatris Specialty LLC, effective May 15, 2026 (SPL set 8512d0c6-db4e-4673-b3b4-28975c18413f), 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
| Mercaptopurine | Olsalazine | |
|---|---|---|
| Labeled for | Leukemia, lymphoma and myeloma | Crohn's disease and ulcerative colitis |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $1.07 per tablet 50 mg tablet | $15.70 per capsule 250 mg capsule |
| Shortage now | No current entry | 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