What the FDA labels say about taking them together
Olsalazine and thioguanine
Olsalazine's FDA label of May 15, 2026 names thioguanine in its drug interactions section, and thioguanine's label names olsalazine too. The olsalazine label: “Azathioprine 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 …”
Check it at the source: the olsalazine FDA label on DailyMed (effective May 15, 2026, Viatris Specialty LLC); the thioguanine FDA label on DailyMed (effective January 8, 2025, Waylis Therapeutics LLC).
What does the olsalazine label say about thioguanine?
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
What does the thioguanine label say about olsalazine?
Thioguanine label, drug interactionsAs there is in vitro evidence that aminosalicylate derivatives (e.g., olsalazine, mesalazine, or sulphasalazine) inhibit the TPMT enzyme, they should be administered with caution to patients receiving concurrent thioguanine therapy (see WARNINGS).
Thioguanine label, warningsBone marrow suppression could be exacerbated by coadministration with drugs that inhibit TPMT, such as olsalazine, mesalazine, or sulphasalazine.
Source: FDA drug label (TABLOID), Waylis Therapeutics LLC, effective January 8, 2025 (SPL set 44b0c461-47fb-4106-ba11-6ed85530235c), 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
| Olsalazine | Thioguanine | |
|---|---|---|
| Labeled for | Crohn's disease and ulcerative colitis | Leukemia, lymphoma and myeloma |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $15.70 per capsule 250 mg capsule | n/a |
| 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