What the FDA labels say about taking them together
Rifampin and tamoxifen
Tamoxifen's FDA label of December 18, 2025 names rifampin in its drug interactions section; the rifampin label PlainMeds reads does not name tamoxifen. The tamoxifen label: “Strong CYP3A4 inducers (e.g., rifampin) reduce tamoxifen AUC and C max.”
Check it at the source: the rifampin FDA label on DailyMed (effective February 11, 2026, Lupin Pharmaceuticals, Inc.); the tamoxifen FDA label on DailyMed (effective December 18, 2025, Actavis Pharma, Inc.).
What does the rifampin label say about tamoxifen?
Rifampin's label (effective February 11, 2026) does not name tamoxifen in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (rifampin), Lupin Pharmaceuticals, Inc., effective February 11, 2026 (SPL set b56004f0-f23d-47f6-80c7-39884fccbccc), via openFDA; the full label on DailyMed
What does the tamoxifen label say about rifampin?
Tamoxifen label, drug interactionsTamoxifen and N-desmethyl tamoxifen plasma concentrations have been shown to be reduced when coadministered with rifampin or aminoglutethimide.
Soltamox label (Mayne Pharma, November 29, 2021), drug interactionsStrong CYP3A4 inducers (e.g., rifampin) reduce tamoxifen AUC and C max [see Clinical Pharmacology (12.3) ].
Source: FDA drug label (Soltamox, NDA021807), Mayne Pharma, effective November 29, 2021 (SPL set 1e6ff055-590c-41e6-9530-1fdf04cdbd02), via openFDA
Source: FDA drug label (Tamoxifen Citrate), Actavis Pharma, Inc., effective December 18, 2025 (SPL set 9b8a4211-120f-4981-ad69-928accb97637), 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
| Rifampin | Tamoxifen | |
|---|---|---|
| Labeled for | n/a | Breast cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.679 per capsule 300 mg capsule | $0.277 per tablet 20 mg tablet |
| Shortage now | In shortage | 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