What the FDA labels say about taking them together
Diphenhydramine and trastuzumab
Trastuzumab's FDA label of May 29, 2026 names diphenhydramine in its warnings and precautions section; the diphenhydramine label PlainMeds reads does not name trastuzumab. The trastuzumab label: “Interrupt Ogivri infusion in all patients experiencing dyspnea, clinically significant hypotension, and intervention of medical therapy administered.”
Check it at the source: the diphenhydramine FDA label on DailyMed (effective November 18, 2025, Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc.); the trastuzumab FDA label on DailyMed (effective May 29, 2026, Genentech, Inc.).
What does the diphenhydramine label say about trastuzumab?
Diphenhydramine's label (effective November 18, 2025) does not name trastuzumab in these sections. A label lists what its studies and reports found; it is not a complete list.
Source: FDA drug label (Diphenhydramine Hydrochloride), Heritage Pharmaceuticals Inc. d/b/a Avet Pharmaceuticals Inc., effective November 18, 2025 (SPL set 6178d3a1-0741-49a4-be81-c4f7d29f8b2a), via openFDA; the full label on DailyMed
What does the trastuzumab label say about diphenhydramine?
Trastuzumab label, warnings and precautionsInterrupt Herceptin infusion in all patients experiencing dyspnea, clinically significant hypotension, and intervention of medical therapy administered (which may include epinephrine, corticosteroids, diphenhydramine, bronchodilators, and oxygen).
Source: FDA drug label (Kanjinti, BLA761073), Amgen, Inc, effective June 23, 2026 (SPL set 9a94f5b2-b84e-4987-8ea1-c4346db5a5fa), via openFDA
Source: FDA drug label (Herzuma, BLA761091), Cephalon, Inc., effective December 22, 2025 (SPL set ae71c003-883a-4cd8-ad50-e8cc9a54e971), via openFDA
Source: FDA drug label (Ogivri, BLA761074), Mylan Institutional LLC, effective February 8, 2021 (SPL set 6b7938e6-14c7-4a65-9605-967542ecfb8f), via openFDA
Source: FDA drug label (Herceptin), Genentech, Inc., effective May 29, 2026 (SPL set 492dbdb2-077e-4064-bff3-372d6af0a7a2), 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
| Diphenhydramine | Trastuzumab | |
|---|---|---|
| Labeled for | Cough and cold, Allergies, Pain | Breast cancer |
| Boxed warning | No | Yes |
| Pharmacy cost (NADAC) | $0.898 per mL 50 mg/mL vial | 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