What the FDA labels say about taking them together
Mercaptopurine and natalizumab
Natalizumab's FDA label (Tyruko) of October 31, 2025 names mercaptopurine in its drug interactions section; the mercaptopurine labels PlainMeds reads (2) do not name natalizumab. The natalizumab label: “DRUG INTERACTIONS Because of the potential for increased risk of PML and other infections, Crohn’s disease patients receiving natalizumab products should not be treated with concomitant immunosuppressants or inhibitors …”
Check it at the source: the mercaptopurine FDA label on DailyMed (effective July 20, 2026, Nova Laboratories, Ltd); the natalizumab FDA label on DailyMed (effective March 21, 2025, Biogen Inc.).
What does the mercaptopurine label say about natalizumab?
Mercaptopurine's label (effective July 20, 2026) and its 1 other brand-application label do not name natalizumab in these sections. A label lists what its studies and reports found; it is not a complete list.
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 natalizumab label say about mercaptopurine?
Tyruko label (Sandoz Inc, October 31, 2025), drug interactionsDRUG INTERACTIONS Because of the potential for increased risk of PML and other infections, Crohn’s disease patients receiving natalizumab products should not be treated with concomitant immunosuppressants (e.g., 6‑ mercaptopurine, azathioprine, cyclosporine, or methotrexate) or inhibitors of TNF-α, and corticosteroids should be tapered in those patients with Crohn’s disease who are on chronic corticosteroids when they start TYRUKO therapy [see Indications and Usage ( 1.2 ) and Warnings and Precautions ( 5.1 , 5.6 )].
Source: FDA drug label (Tyruko, BLA761322), Sandoz Inc, effective October 31, 2025 (SPL set ef653c36-dd4b-4e71-9d2d-40b8fea24b67), via openFDA
Source: FDA drug label (TYSABRI), Biogen Inc., effective March 21, 2025 (SPL set c5fdde91-1989-4dd2-9129-4f3323ea2962), 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 | Natalizumab | |
|---|---|---|
| Labeled for | Leukemia, lymphoma and myeloma | Multiple sclerosis |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $1.07 per tablet 50 mg tablet | 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