Meds A-Z
Diphenhydramine
Detailed information about Diphenhydramine
Pet Owner Quick Guide
Start here: what this medicine is for, what it does, and when it's usually needed.
Usually used for:
Antihistamine sometimes used for allergies/itching and mild allergic reactions; may cause mild sedation.
What it does:
Antihistamine sometimes used for allergies/itching and mild allergic reactions; may cause mild sedation.
When it's needed:
Use caution with glaucoma, urinary retention, or certain cardiac conditions.
Call your vet sooner if you notice:
- Use caution with glaucoma, urinary retention, or certain cardiac conditions.
Commonly reported reactions:
- (2 reports)
- (1 reports)
- (1 reports)
What to ask your vet today:
- Is this medicine the right fit for my pet’s current symptoms?
- Which warning signs mean I should call back right away?
- How should I handle missed doses or refusal to take the medicine?
Diphenhydramine
Drug type: Generic ingredient • Generic profile • No FDA branded products linked
Species: Both
Manufacturer: MSK
Quick Facts
Official label facts first, then secondary summaries. Marketing content is separated below.
Warnings / Contraindications
Use caution with glaucoma, urinary retention, or certain cardiac conditions.
- High: Use caution with glaucoma, urinary retention, or certain cardiac conditions.
- https://animaldrugsatfda.fda.gov · safety_warning · Medication contraindications
Adverse Reactions
Snapshot first, detailed rows second. This section summarizes signal data and is not a diagnosis.
Tap or hover a reaction to see what it means in plain language.
Most Reported Reactions
| Reaction | Cases | Species | Serious cases |
|---|---|---|---|
| 2 | Cat, Dog | 2 | |
| 1 | Cat | 1 | |
| 1 | Cat | 1 | |
| 1 | Dog | 1 | |
| 1 | Cat | 1 | |
| 1 | Cat | 1 | |
| 1 | Cat | 1 | |
| 1 | Dog | 1 |
Species coverage: Cat (20) Dog (12)
View detailed reaction table
| Reaction | Species | Seriousness | Frequency | Reports |
|---|---|---|---|---|
| Dog | Serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Dog | Non-serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Dog | Non-serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Dog | Non-serious | - | 1 | |
| Dog | Serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Non-serious | - | 1 | |
| Cat | Serious | - | 1 | |
| Cat | Serious | - | 1 |
- https://api.fda.gov/animalandveterinary/event.json · adverse_reaction · openFDA case USA-USFDACVM-2025-US-054865
Storage & Handling
Store at room temperature.
Documents
Official label facts are separated from secondary summaries.
No linked label PDFs or safety notices yet.
No source yet.
No source yet.
Promotional Materials (Marketing)
This content is marketing material and not clinical guidance.
No marketing assets are linked yet.
No source yet.
Technical appendix (vet reference)
Canonical medication sections are above. This legacy block remains available for deeper cross-reference without cluttering the primary workflow.
At a Glance
Quick facts and links to official labeling and safety signals.
- Medication catalog: Source PetWisePlus | Refreshed Feb 12, 2026, 7:40 PM UTC
-
Animal Drug Product Listing Directory (NDC):
Source FDA
| Refreshed Feb 16, 2026, 11:00 AM UTC
Package/product NDCs from FDA’s electronic listing directory (XLS).
- openFDA reaction terms: Source FDA openFDA | Refreshed Feb 16, 2026, 11:02 AM UTC
- openFDA case summaries: Source FDA openFDA | Refreshed Feb 9, 2026, 3:19 AM UTC
Diagnosis-code mappings are not available for this medication yet.
Counseling and Monitoring Highlights
Global Pet owner/Vet mode is controlled in the header. This section avoids duplicate in-page persona tabs.
- Use caution with glaucoma, urinary retention, or certain cardiac conditions. (Contraindication, High)
Identifiers & Packages
Normalized identifiers (NDC/NADA/ANADA) and package metadata from regulator listings.
| Package NDC | Product NDC | Form / Route | Status |
|---|---|---|---|
| 21091-695-01 | 21091 | - | |
| 43655-002-01 | 43655 | - | |
| 49427-329-45 | 49427 | - | |
| 49427-329-57 | 49427 | - | |
| 49427-330-45 | 49427 | - | |
| 49427-330-57 | 49427 | - | |
| 70782-200-08 | 70782 | - | |
| 70782-201-12 | 70782 | - | |
| 72087-021-10 | 72087 | - | |
| 72087-022-20 | 72087 | - | |
| 80547-116-50 | 80547 | - | |
| 80547-128-50 | 80547 | - |
Data Sources & Revision History
Every non-trivial field is expected to include provenance and update timestamps.
- contraindications: Use caution with glaucoma, urinary retention, or certain cardiac conditions. (Clinical, 2026-02-12)
- overdose_info: Overdose causes extreme drowsiness, tremors, seizures, or hyperexcitability. In severe cases, respiratory failure is possible. Treat with IV fluids, seizure co… (Clinical, 2026-02-12)
- storage_handling: Store at room temperature. (Clinical, 2026-02-12)
- usage: Antihistamine sometimes used for allergies/itching and mild allergic reactions; may cause mild sedation. (Clinical, 2026-02-12)
- side_effects: Sedation, dry mouth, GI upset; occasional paradoxical excitement. (Official, 2026-02-12)
- side_effects updated 2026-02-12 19:40 by etl_backfill • Backfilled from existing medication fields
- contraindications updated 2026-02-12 19:40 by etl_backfill • Backfilled from existing medication fields
- usage updated 2026-02-12 19:40 by etl_backfill • Backfilled from existing medication fields
FDA Products & Applications (Animal Drugs @ FDA)
No linked FDA product applications are available for this ingredient yet.
Usage
Antihistamine sometimes used for allergies/itching and mild allergic reactions; may cause mild sedation.
Contraindications
Use caution with glaucoma, urinary retention, or certain cardiac conditions.
Side Effects
Sedation, dry mouth, GI upset; occasional paradoxical excitement.
Source: FDA openFDA • Reference
Top Reported Reactions (openFDA)
Aggregated reaction terms from FDA openFDA reports (not verified; does not prove causation).
Data source: FDA openFDA Animal & Veterinary adverse event reports.
Adverse Event Case Summaries (openFDA)
These are individual FDA adverse event reports. They are unverified and do not prove the medication caused the reaction.
Cat, Snowshoe, Male, 1 year, 4.264 kilogram • Drug: MSK, Intramuscular, Dose: 0.20 mL per animal • Reactions: Vomiting, Blood in vomit, Death, Anaphylaxis • Outcome: Died
- Report ID: USA-USFDACVM-2025-US-055626
- Serious AE: Yes
- Treated For AE: Yes
- Sex: Male
- Age: 1.00 Year
- Weight: 4.264 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Intramuscular
- Dose: 0.20 mL per animal
Dog, Poodle (unspecified), Male, 4 year, 9.5 kilogram • Drug: MSK, Unassigned, Intramuscular • Reactions: Vomiting, Pain NOS, Whining, Lack of efficacy - NOS • Outcome: Ongoing
- Report ID: USA-USFDACVM-2025-US-054507
- Serious AE: Yes
- Treated For AE: Yes
- Sex: Male
- Age: 4.00 Year
- Weight: 9.500 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Intramuscular
- Form: Unassigned
Dog, Terrier - Yorkshire, Female, 9.08 year, 4.5 kilogram • Drug: MSK, Unknown • Reactions: Weight gain, Lack of efficacy - NOS • Outcome: Ongoing
- Report ID: USA-USFDACVM-2025-US-055408
- Serious AE: No
- Treated For AE: No
- Sex: Female
- Age: 9.08 Year
- Weight: 4.500 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Unknown
Dog, Retriever - Labrador, Male, 11 year, 33.747 kilogram • Drug: MSK, Injection, Unknown, Dose: 1 dose per animal, Frequency: 1 per day • Reactions: Diarrhea, Injection site discharge NOS • Outcome: Outcome Unknown
- Report ID: USA-USFDACVM-2025-US-055855
- Serious AE: No
- Treated For AE: No
- Sex: Male
- Age: 11.00 Year
- Weight: 33.747 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Unknown
- Form: Injection
- Dose: 1 dose per animal
- Frequency: 1 per day
Dog, Terrier - Bull - American Pit, Male, 1 year, 39.463 kilogram • Drug: MSK, Unassigned, Unknown • Reactions: Mast cell tumour, Pododermatitis, Bumps on skin, Pyoderma, Ear infection NOS… • Outcome: Ongoing
- Report ID: USA-USFDACVM-2025-US-054865
- Serious AE: Yes
- Treated For AE: Yes
- Sex: Male
- Age: 1.00 Year
- Weight: 39.463 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Unknown
- Form: Unassigned
Dog, Terrier - Boston, Female, 13 year, 9.979 kilogram • Drug: MSK, Unassigned, Unknown • Reactions: Facial swelling (possible allergy), Head tilt - neurological disorder, Staggering • Outcome: Ongoing
- Report ID: USA-USFDACVM-2025-US-055030
- Serious AE: Yes
- Treated For AE: Yes
- Sex: Female
- Age: 13.00 Year
- Weight: 9.979 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Unknown
- Form: Unassigned
Cat, Domestic Shorthair, Female, 13 year, 2.81 kilogram • Drug: MSK, Parenteral • Reactions: Unsteady walking (ataxia), Loss of appetite, Vomiting, Fever, Pain NOS… • Outcome: Recovered/Normal
- Report ID: USA-USFDACVM-2025-US-053912
- Serious AE: No
- Treated For AE: Yes
- Sex: Female
- Age: 13.00 Year
- Weight: 2.810 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Parenteral
Cat, Domestic Longhair, Female, 1 year, 4.1 kilogram • Drug: MSK, Injection, Unknown • Reactions: Foaming at the mouth, Tongue disorder NOS, Dullness, Behavioral disorder (unspecified), Not drinking… • Outcome: Recovered/Normal
- Report ID: USA-USFDACVM-2025-US-052856
- Serious AE: No
- Treated For AE: No
- Sex: Female
- Age: 1.00 Year
- Weight: 4.100 Kilogram
- Case-reported brand: MSK
- Case-reported manufacturer: MSK
- Route: Unknown
- Form: Injection
Data source: FDA openFDA Animal & Veterinary adverse event reports.
Overdose Information
Overdose causes extreme drowsiness, tremors, seizures, or hyperexcitability. In severe cases, respiratory failure is possible. Treat with IV fluids, seizure control.
Storage & Handling
Store at room temperature.
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This medication has not been reviewed by a veterinarian yet.