Benadryl (Diphenhydramine) For Cats

At a glance

  • Drug Name: Diphenhydramine hydrochloride
  • Common names: Benadryl, Dimedrol, Daedalon, Nytol, Vetadryl
  • Drug Type: First-generation antihistamine
  • Used For: Allergies, motion sickness, mast cell tumours, vaccine and blood transfusion reactions
  • Species: Humans, cats, dogs, ferrets, rabbits, rodents, birds and cattle
  • Administered: Tablet, oral liquid, injection

What is Benadryl?

Benadryl (diphenhydramine hydrochloride) is a first-generation antihistamine that blocks the effects of histamine by preventing it from attaching to H1 receptors on the small blood vessels and smooth muscles. Histamine is a chemical compound released by mast cells which are responsible for many allergy symptoms.


  • Allergies
  • Insect bites and stings
  • Rashes
  • Motion sickness
  • Nasal congestion
  • Mast cell tumours
  • Vaccine or blood transfusion reaction

Dosage chart

1 milligram (mg) per pound, or 2 mg per kilo, twice a day. Due to the bitter taste, some cats will be reluctant to medicate; a compounding pharmacy can make a preparation to flavour the drug which makes it more palatable for cats.

Always check with your veterinarian before giving any medications to your cat and check the packaging to determine the strength of the medication.

There is no specific cat Benadryl; the medication for cats is the same as the medication for people and is available from any chemist. There may be generic versions of Benadryl (which is a registered trademark of Johnson and Johnson). Make sure the only active ingredient is diphenhydramine hydrochloride as some preparations may also contain more than one active ingredient which can lead to severe poisoning in cats.

Side effects

All medications have potential side effects, the most commonly seen adverse effects are CNS depression (lethargy) and anticholinergic effects (urinary retention and dry mouth). Less common side effects include:

If your cat experiences any of the following, contact your veterinarian for advice.

Do not give Benadryl to cats who are allergic to diphenhydramine hydrochloride.

Drug interactions

Benadryl may react with the following medications:

  • Selegiline
  • Epinephrine
  • Heparin sodium or calcium
  • Warfarin sodium
  • Amitraz
  • Furazolidone


Do not give Benadryl to cats with the following conditions:

In humans, Benadryl has been categorised as a category B drug by the FDA which means it is safe to use in pregnancy, but it is always important to check with your veterinarian before administering Benadryl to a pregnant or lactating cat.

How is Benadryl supplied?

Benadryl is available as a tablet, oral liquid or injectable.

  • Oral tablets: 10 mg, 12.5 mg, 25 mg, 50 mg.
  • Oral liquid: 12.5 mg per 5ml.
  • Injectable: 50 mg per millilitre.


Seek immediate veterinary attention if you suspect your cat has had too much Benadryl.

Frequently asked questions

Is Benadryl safe for cats?

Under the guidance of a veterinarian, Benadryl is a safe medication with few side-effects.

How long does it take Benadryl to work?

Benadryl is a fast-acting medication and usually takes effect within 30 minutes.

My cat is foaming at the mouth after Benadryl

Benadryl is bitter tasting and foaming at the mouth is common after administration. Offer the cat a drink of water or a tasty treat to help get rid of the taste.

What kind of Benadryl can I give my cat?

Most pet owners choose the liquid form of Benadryl which is easier to administer than tablets. But either type is suitable for cats.

Can Benadryl kill a cat?

Yes, it is possible if the cat receives a dose higher than the recommended dose if the cat has an allergic reaction to diphenhydramine hydrochloride or in cats with underlying medical conditions which contraindicate its use.

It is always recommended that pet owners speak to a veterinarian before administering any over the counter or non-prescribed medication.

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