What the FDA labels say about taking them together
Allopurinol and fluorouracil
Allopurinol's FDA label of May 21, 2026 names fluorouracil in its drug interactions section; the fluorouracil labels PlainMeds reads (4) do not name allopurinol. The allopurinol label: “Fluorouracil Clinical Impact Based on non-clinical data, allopurinol may decrease anti-tumor activity due to suppression of phosphorylation of 5-fluorouracil. …”
Check it at the source: the allopurinol FDA label on DailyMed (effective May 21, 2026, Rising Pharma Holdings, Inc.); the fluorouracil FDA label on DailyMed (effective January 19, 2026, Eugia US LLC).
What does the allopurinol label say about fluorouracil?
Allopurinol label, drug interactionsFluorouracil Clinical Impact Based on non-clinical data, allopurinol may decrease anti-tumor activity due to suppression of phosphorylation of 5-fluorouracil. Intervention Concomitant administration with fluorouracil should be avoided.
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 fluorouracil label say about allopurinol?
Fluorouracil's label (effective January 19, 2026) and its 3 other brand-application labels do not name allopurinol in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (FLUOROURACIL), Eugia US LLC, effective January 19, 2026 (SPL set 697816ce-dc05-4943-b7f0-2f0b125e93b7), 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 | Fluorouracil | |
|---|---|---|
| Labeled for | Gout | Colorectal cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.0315 per tablet 100 mg tablet | $0.616 per gram 5% cream |
| 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