What the FDA labels say about taking them together
Mercaptopurine and sulfasalazine
Mercaptopurine's FDA label (Mercaptopurine) of January 30, 2026 names sulfasalazine in its drug interactions section; the sulfasalazine label PlainMeds reads does not name mercaptopurine. 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 sulfasalazine FDA label on DailyMed (effective May 29, 2026, Pfizer Laboratories Div Pfizer Inc).
What does the mercaptopurine label say about sulfasalazine?
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 sulfasalazine label say about mercaptopurine?
Sulfasalazine's label (effective May 29, 2026) does not name mercaptopurine in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Azulfidine), Pfizer Laboratories Div Pfizer Inc, effective May 29, 2026 (SPL set ddbe69f3-bd55-45f3-a64f-f60226c744c4), 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 | Sulfasalazine | |
|---|---|---|
| Labeled for | Leukemia, lymphoma and myeloma | Crohn's disease and ulcerative colitis, Rheumatoid arthritis |
| Boxed warning | No | No |
| Pharmacy cost (NADAC) | $1.07 per tablet 50 mg tablet | $0.199 per tablet 500 mg tablet |
| 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