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PetDosageChart

Benadryl (Diphenhydramine) Dosage for Cats

Antihistamine ⏱ Onset: 30-60 minutes ⏳ Duration: 8-12 hours

This dosage information is for educational purposes only. Always consult your veterinarian before giving any medication to your pet. Dosages may vary based on your pet's health conditions, other medications, and individual factors.

Content reviewed by licensed veterinarians. This information is sourced from veterinary drug references including Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

Dosage Calculator

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Benadryl Dosage Chart for Cats by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
3 lbs (1.4 kg) 1.5mg 3mg 5.5mg every 8-12 hours
4 lbs (1.8 kg) 2mg 3.5mg 7mg every 8-12 hours
5 lbs (2.3 kg) 2.5mg 4.5mg 9mg every 8-12 hours
6 lbs (2.7 kg) 2.5mg 5.5mg 11mg every 8-12 hours
7 lbs (3.2 kg) 3mg 6.5mg 13mg every 8-12 hours
8 lbs (3.6 kg) 3.5mg 7mg 14.5mg every 8-12 hours
9 lbs (4.1 kg) 4mg 8mg 16.5mg every 8-12 hours
10 lbs (4.5 kg) 4.5mg 9mg 18mg every 8-12 hours
12 lbs (5.4 kg) 5.5mg 11mg 21.5mg (25mg tablet) every 8-12 hours
14 lbs (6.3 kg) 6.5mg 12.5mg 25mg (25mg tablet) every 8-12 hours
16 lbs (7.3 kg) 7.5mg 14.5mg 29mg (25mg tablet) every 8-12 hours
18 lbs (8.2 kg) 8mg 16.5mg 33mg every 8-12 hours
20 lbs (9.1 kg) 9mg 18mg 36.5mg every 8-12 hours
25 lbs (11.3 kg) 11.5mg 22.5mg (25mg tablet) 45mg (2 × 25mg) every 8-12 hours

What is Benadryl (Diphenhydramine) used for in cats?

allergies itching motion sickness vaccine reactions

How to give Benadryl to your cat

Pilling cats can be challenging. Use a pill pocket, hide in a small amount of wet food, or use a pill gun. Use plain diphenhydramine only — never formulations with decongestants or pain relievers. Liquid formulations may contain xylitol. A typical cat dose is about half of a 25 mg tablet (12.5 mg) but consult your vet.

Available Forms

tablet, liquid

Give with Food?

Yes — give with food

Side effects of Benadryl in cats

Common side effects

drowsiness
dry mouth
decreased appetite
hyperexcitability (paradoxical in some cats)

Serious side effects

  • rapid heartbeat
  • difficulty breathing
  • severe sedation
  • urinary retention

When to call the vet

Call your vet immediately if your cat shows any of these signs:

  • Extreme excitement or agitation instead of sedation
  • Difficulty breathing
  • Rapid or irregular heartbeat
  • Inability to urinate
  • Seizures or tremors

Related Medications for Cats

First-generation antihistamine

Chlor-Trimeton

Chlorpheniramine

For allergies

View dosage chart
Antihistamine (H1 Receptor Antagonist)

Atarax

Hydroxyzine

For Allergic dermatitis and itching

View dosage chart
Second-Generation Antihistamine (H1 Receptor Antagonist)

Claritin

Loratadine

For Allergic dermatitis

View dosage chart
Second-Generation Antihistamine (H1 Receptor Antagonist)

Zyrtec

Cetirizine

For Allergic dermatitis and itching

View dosage chart

Sources & References

The dosage information on this page is compiled from the following veterinary and pharmaceutical references:

  • Plumb's Veterinary Drug Handbook — the standard veterinary pharmacology reference used by veterinarians worldwide.
  • Merck Veterinary Manual — a trusted, peer-reviewed resource for veterinary professionals and pet owners.
  • DailyMed (FDA Drug Labels) — official FDA-approved drug labeling and prescribing information for Diphenhydramine.

Frequently Asked Questions

Can I give my cat Benadryl?
Yes, Benadryl (diphenhydramine) can be given to cats for allergies and mild allergic reactions, but only under veterinary guidance. Cats are smaller and more sensitive to medications than dogs, so accurate dosing is critical. Use plain diphenhydramine only.
How much Benadryl can I give my cat?
The typical dose for cats is 1-2 mg per kg of body weight, given every 8-12 hours. For an average 10 lb (4.5 kg) cat, this is approximately half of a 25 mg tablet (12.5 mg). Always confirm the dose with your veterinarian.
Why is my cat acting hyper after Benadryl?
Some cats experience a paradoxical reaction to antihistamines, becoming hyperactive or agitated instead of drowsy. This is more common in cats than dogs. If your cat reacts this way, discontinue Benadryl and consult your vet for alternative antihistamines.
Is liquid Benadryl safe for cats?
Be very cautious with liquid Benadryl for cats. Many liquid formulations contain alcohol, xylitol, or other additives that can be harmful to cats. If you need a liquid option, ask your vet for a veterinary-compounded liquid with safe ingredients.

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