What the FDA labels say about taking them together
Ribociclib and tamoxifen
Ribociclib's FDA label of July 1, 2026 names tamoxifen in its warnings and precautions section; the tamoxifen labels PlainMeds reads (2) do not name ribociclib. The ribociclib label: “Avoid using KISQALI with drugs known to prolong QT interval and/or strong CYP3A inhibitors. Increased QT Prolongation with Concomitant Use of Tamoxifen:”
Check it at the source: the ribociclib FDA label on DailyMed (effective July 1, 2026, Novartis Pharmaceuticals Corporation); the tamoxifen FDA label on DailyMed (effective December 18, 2025, Actavis Pharma, Inc.).
What does the ribociclib label say about tamoxifen?
Ribociclib label, warnings and precautionsAvoid using KISQALI with drugs known to prolong QT interval and/or strong CYP3A inhibitors. ( 2.2 , 5.3 , 7.1 , 7.4 ) Increased QT Prolongation with Concomitant Use of Tamoxifen:
Source: FDA drug label (KISQALI), Novartis Pharmaceuticals Corporation, effective July 1, 2026 (SPL set aaeaef94-f3f5-4367-8ea2-b181d7be2da8), via openFDA; the full label on DailyMed
What does the tamoxifen label say about ribociclib?
Tamoxifen's label (effective December 18, 2025) and its 1 other brand-application label do not name ribociclib in these sections. A label lists what its studies and reports found; it is not a complete list.
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
| Ribociclib | Tamoxifen | |
|---|---|---|
| Labeled for | Breast cancer | Breast cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $289.72 per unit 600 mg daily dose | $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