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Diphenhydramine

Detailed information about Diphenhydramine

Official label facts Owner quick guide first Marketing clearly labeled
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Reviewed / Updated / Sources

Reviewed: Not available

Updated: February 12, 2026, 7:40 PM UTC

Sources:

Pet Owner Quick Guide

Start here first for the simple next-step summary.

Used for:

Antihistamine sometimes used for allergies/itching and mild allergic reactions; may cause mild sedation.

What to watch for:

  • Use caution with glaucoma, urinary retention, or certain cardiac conditions
  • Vomiting (1 reports)
  • Overdose (1 reports)
  • Open mouth breathing (1 reports)

When to call the vet:

  • Repeated vomiting or diarrhea.
  • Severe lethargy (hard to wake, very low energy).
  • Collapse or fainting.
  • Trouble breathing.
  • Facial swelling or hives.
  • Blood in vomit or stool.

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?
Safety & side effects

What to watch:

  • Use caution with glaucoma, urinary retention, or certain cardiac conditions
  • Vomiting
  • Overdose
  • Open mouth breathing

Most reported reactions:

  • Vomiting (1 reports)
  • Overdose (1 reports)
  • Open mouth breathing (1 reports)

When to call your vet:

  • Repeated vomiting or diarrhea.
  • Severe lethargy (hard to wake, very low energy).
  • Collapse or fainting.
  • Trouble breathing.
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Data freshness: source data appears current.

Latest refresh: Mar 21, 2026, 10:02 a.m.

Data freshness
  • Medication catalog: Source Roxee | Refreshed Feb 12, 2026, 7:40 PM UTC
  • Animal Drug Product Listing Directory (NDC): Source FDA | Refreshed Mar 21, 2026, 10:01 AM UTC
    Package/product NDCs from FDA’s electronic listing directory (XLS).
  • openFDA reaction terms: Source FDA openFDA | Refreshed Mar 21, 2026, 10:02 AM UTC
  • openFDA case summaries: Source FDA openFDA | Refreshed Feb 9, 2026, 3:19 AM UTC
Image for Diphenhydramine

Diphenhydramine

Drug type: Generic ingredient • Generic profile • No FDA branded products linked

Species: Both

Manufacturer: Not available (source)

Quick Facts

Official label facts first, then secondary summaries. Marketing content is separated below.

Species: Both
Manufacturer: Not available
Identifiers:
NDC Package: 21091-695-01 NDC Package: 43655-002-01 NDC Package: 49427-329-45 NDC Package: 49427-329-57 NDC Package: 49427-330-45 NDC Package: 49427-330-57 NDC Package: 70782-200-08 NDC Package: 70782-201-12 NDC Package: 72087-021-10 NDC Package: 72087-022-20 NDC Package: 80547-116-50 NDC Package: 80547-128-50 NDC Product: 21091 NDC Product: 43655 NDC Product: 49427 NDC Product: 70782 NDC Product: 72087 NDC Product: 80547

Warnings / Contraindications

Use caution with glaucoma, urinary retention, or certain cardiac conditions.

  • High: Use caution with glaucoma, urinary retention, or certain cardiac conditions.
Source metadata:

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.

Tracked signals
32
Reported cases
32
Serious reports
19
Species represented
2
Grouped by Body System
Digestive (6) · Vomiting, Nausea, Loss of appetite Skin & allergy (2) · Hair loss, Facial swelling (possible allergy) Neurologic (2) · Unsteady walking (ataxia), Head tilt - neurological disorder Behavior (1) · Behavioral disorder (unspecified) Effectiveness (1) · Lack of efficacy - NOS Other (20) · Overdose, Open mouth breathing, Not eating
Most Reported Reactions
Reaction Body system Cases Species Serious cases
Digestive 1 Cat 1
Other 1 Dog 1
Other 1 Cat 1
Other 1 Cat 1
Other 1 Dog 1
Other 1 Cat 1
Other 1 Cat 1
Other 1 Cat 1

Species coverage: Cat (20) Dog (12)

View detailed reaction table
Reaction Body system Species Seriousness Frequency Reports
Digestive Cat Serious - 1
Neurologic Cat Non-serious - 1
Other Dog Serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Other Cat Non-serious - 1
Digestive Cat Non-serious - 1
Other Dog Serious - 1
Digestive Cat Non-serious - 1
Effectiveness Dog Non-serious - 1
Other Cat Serious - 1
Other Dog Non-serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Neurologic Dog Serious - 1
Skin & allergy Dog Serious - 1
Other Cat Non-serious - 1
Other Cat Non-serious - 1
Other Cat Non-serious - 1
Skin & allergy Dog Serious - 1
Other Dog Serious - 1
Other Dog Serious - 1
Other Cat Non-serious - 1
Digestive Dog Non-serious - 1
Digestive Cat Non-serious - 1
Other Cat Serious - 1
Other Dog Serious - 1
Other Dog Serious - 1
Digestive Cat Serious - 1
Behavior Cat Non-serious - 1
Other Cat Serious - 1
Other Cat Serious - 1
Source metadata:

Storage & Handling

Store at room temperature.

Veterinary reference (advanced)

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.

Data freshness
  • Medication catalog: Source Roxee | Refreshed Feb 12, 2026, 7:40 PM UTC
  • Animal Drug Product Listing Directory (NDC): Source FDA | Refreshed Mar 21, 2026, 10:01 AM UTC
    Package/product NDCs from FDA’s electronic listing directory (XLS).
  • openFDA reaction terms: Source FDA openFDA | Refreshed Mar 21, 2026, 10:02 AM UTC
  • openFDA case summaries: Source FDA openFDA | Refreshed Feb 9, 2026, 3:19 AM UTC
Official (FDA)
Identity: Generic ingredient • No FDA branded products linked
No official FDA brand rows linked yet for this ingredient.
Case-reported brands (openFDA): MSK
Catalog species: Both
Safety (openFDA)
Top reactions: Dog 29 • Cat 15 • View
Case summaries: 10 (showing 8) • View
openFDA reports are unverified and do not prove causation.
Diagnosis Codes

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.

Owner-facing counseling points
  • Use caution with glaucoma, urinary retention, or certain cardiac conditions. (Contraindication, High)
Top reaction signals
Vomiting (1) Overdose (1) Open mouth breathing (1) Not eating (1) Mast cell tumour (1) Intentional misuse (1) Increased respiratory rate (1) Incorrect route of drug administration (1)

Identifiers & Packages

Normalized identifiers (NDC/NADA/ANADA) and package metadata from regulator listings.

Identifiers
NDC Package: 21091-695-01 NDC Package: 43655-002-01 NDC Package: 49427-329-45 NDC Package: 49427-329-57 NDC Package: 49427-330-45 NDC Package: 49427-330-57 NDC Package: 70782-200-08 NDC Package: 70782-201-12 NDC Package: 72087-021-10 NDC Package: 72087-022-20 NDC Package: 80547-116-50 NDC Package: 80547-128-50 NDC Product: 21091 NDC Product: 43655 NDC Product: 49427 NDC Product: 70782 NDC Product: 72087 NDC Product: 80547
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 & Change Log

Every non-trivial field is expected to include provenance and update timestamps.

Official 1 Clinical 4 Manufacturer 0 Marketing 0
Current Field Facts
  • 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)
Recent Revisions
  • 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

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)

De-duplicated reaction terms grouped by body system from FDA openFDA reports (not verified; does not prove causation).

Digestive
Vomiting (1) • Cat Nausea (1) • Cat Loss of appetite (1) • Cat Diarrhea (1) • Dog Decreased appetite (1) • Cat
Show more (1)
Blood in vomit (1) • Cat

Showing top 5 for Digestive.

Skin & allergy
Hair loss (1) • Dog Facial swelling (possible allergy) (1) • Dog

Showing top 5 for Skin & allergy.

Neurologic
Unsteady walking (1) • Cat Head tilt - neurological disorder (1) • Dog

Showing top 5 for Neurologic.

Behavior
Behavioral disorder (1) • Cat

Showing top 5 for Behavior.

Effectiveness
Lack of efficacy - NOS (1) • Dog

Showing top 5 for Effectiveness.

Other
Overdose (1) • Dog Open mouth breathing (1) • Cat Not eating (1) • Cat Not drinking (1) • Cat Mast cell tumour (1) • Dog
Show more (15)
Intentional misuse (1) • Cat Injection site discharge NOS (1) • Dog Increased respiratory rate (1) • Cat Incorrect route of drug administration (1) • Cat Gagging (1) • Cat Foaming at the mouth (1) • Cat Fever (1) • Cat Epidermal collarette (1) • Dog Ear infection NOS (1) • Dog Dullness (1) • Cat Death (1) • Cat Crust (1) • Dog Bumps on skin (1) • Dog Aspiration pneumonia (1) • Cat Anaphylaxis (1) • Cat

Showing top 5 for Other.

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
Reactions Reported:
Vomiting Blood in vomit Death Anaphylaxis
Outcomes: Died

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
Reactions Reported:
Vomiting Pain NOS Whining Lack of efficacy - NOS
Outcomes: Ongoing

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
Reactions Reported:
Weight gain Lack of efficacy - NOS
Outcomes: Ongoing

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
Reactions Reported:
Diarrhea Injection site discharge NOS
Outcomes: Outcome Unknown

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
Reactions Reported:
Mast cell tumour Pododermatitis Bumps on skin Pyoderma Ear infection NOS Itching Overdose Epidermal collarette Swelling NOS Hair loss Crust
Outcomes: Ongoing

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
Reactions Reported:
Facial swelling (possible allergy) Head tilt - neurological disorder Staggering
Outcomes: Ongoing

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
Reactions Reported:
Unsteady walking (ataxia) Loss of appetite Vomiting Fever Pain NOS Vocalisation Gagging Nausea
Outcomes: Recovered/Normal

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
Reactions Reported:
Foaming at the mouth Tongue disorder NOS Dullness Behavioral disorder (unspecified) Not drinking Decreased appetite
Outcomes: Recovered/Normal

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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