What the FDA labels say about taking them together
Letrozole and tamoxifen
Letrozole's FDA label of June 11, 2026 names tamoxifen in its drug interactions section, and tamoxifen's label names letrozole too. The tamoxifen label: “Tamoxifen reduced letrozole plasma concentrations by 37%.”
Check it at the source: the letrozole FDA label on DailyMed (effective June 11, 2026, Novartis Pharmaceuticals Corporation); the tamoxifen FDA label on DailyMed (effective December 18, 2025, Actavis Pharma, Inc.).
What does the letrozole label say about tamoxifen?
Letrozole label, drug interactionsDRUG INTERACTIONS Tamoxifen Coadministration of Femara and tamoxifen 20 mg daily resulted in a reduction of letrozole plasma levels of 38% on average (Study P015).
Letrozole label, warnings and precautionsResults of a safety study to evaluate safety in the adjuvant setting comparing the effect on lumbar spine (L2-L4) BMD of adjuvant treatment with letrozole to that with tamoxifen showed at 24 months a median decrease in lumbar spine BMD of 4.1% in the letrozole arm compared to a median increase of 0.3% in the tamoxifen arm (difference = 4.4%) ( P < 0.0001) [ s ee Adverse Reactions (6)].
Source: FDA drug label (Femara), Novartis Pharmaceuticals Corporation, effective June 11, 2026 (SPL set 82b77d74-085f-45ac-a7dd-1f5c038bf406), via openFDA; the full label on DailyMed
What does the tamoxifen label say about letrozole?
Tamoxifen label, drug interactionsTamoxifen reduced letrozole plasma concentrations by 37%.
Soltamox label (Mayne Pharma, November 29, 2021), drug interactionsDRUG INTERACTIONS Anastrozole and letrozole: Should not be used in combination with tamoxifen.
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
| Letrozole | Tamoxifen | |
|---|---|---|
| Labeled for | Breast cancer | Breast cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.145 per tablet 2.5 mg tablet | $0.277 per tablet 20 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