Antihistamine · For Cats

Benadryl dosage reference for cats (Diphenhydramine)

This page's standard weight-based reference is 2 mg per kg (0.91 mg per lb), with every 8-12 hours recorded as the reference frequency. Use the calculator to see the arithmetic for your cat's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset: 30-60 minutes
Duration: 8-12 hours
Class: Antihistamine

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Diphenhydramine (often known by brand names such as Benadryl) is an antihistamine commonly used in veterinary medicine for allergies, itching, motion sickness, and vaccine reactions. Understanding the correct dosage, administration, and potential side effects of Diphenhydramine is critical for your cat’s safety and well-being.

A typical Diphenhydramine dose for cats is around 2 mg/kg every 8-12 hours, within a usual range of 1-4 mg/kg. Available forms include tablet and liquid.

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

Diphenhydramine Dosage Calculator for Cats

Enter your cat’s weight below to estimate the Diphenhydramine dose from the 2 mg/kg guideline. Your veterinarian may adjust it for your cat’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your cat's weight

Quick Dosage Chart

Typical Diphenhydramine amounts for common cat weights, for quick reference:

Dosage Chart · 02

Benadryl weight-based reference chart for cats

Scroll sideways to see full table

Weight	Lower Reference	Standard Reference	Upper Reference	Frequency
3 lbs (1.4 kg)	1.4 mg	2.8 mg	5.6 mg	every 8-12 hours
4 lbs (1.8 kg)	1.8 mg	3.6 mg	7.2 mg	every 8-12 hours
5 lbs (2.3 kg)	2.3 mg	4.6 mg	9.2 mg	every 8-12 hours
6 lbs (2.7 kg)	2.7 mg	5.4 mg	10.8 mg	every 8-12 hours
7 lbs (3.2 kg)	3.2 mg	6.4 mg	12.8 mg	every 8-12 hours
8 lbs (3.6 kg)	3.6 mg	7.2 mg	14.4 mg	every 8-12 hours
9 lbs (4.1 kg)	4.1 mg	8.2 mg	16.4 mg	every 8-12 hours
10 lbs (4.5 kg)	4.5 mg	9.0 mg	18.0 mg	every 8-12 hours
12 lbs (5.4 kg)	5.4 mg	10.8 mg	21.6 mg (25mg tablet)	every 8-12 hours
14 lbs (6.3 kg)	6.3 mg	12.6 mg	25.2 mg (25mg tablet)	every 8-12 hours
16 lbs (7.3 kg)	7.3 mg	14.6 mg	29.2 mg (25mg tablet)	every 8-12 hours
18 lbs (8.2 kg)	8.2 mg	16.4 mg	32.8 mg	every 8-12 hours
20 lbs (9.1 kg)	9.1 mg	18.2 mg	36.4 mg	every 8-12 hours
25 lbs (11.3 kg)	11.3 mg	22.6 mg (25mg tablet)	45.2 mg (2 × 25mg)	every 8-12 hours

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Benadryl reference by cat weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

Embed this calculator on your site

Get a free Diphenhydramine dosage widget

Get embed code

Free forever. Works in any blog post or article. Adds a small "Powered by petdosagechart.com" credit at the bottom.

Width Theme

How to Give Diphenhydramine 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.

It is generally recommended to give Diphenhydramine with food to help reduce stomach upset. It may interact with CNS depressants, anticholinergic drugs, and MAO inhibitors.

Side Effects and Safety

Common side effects include drowsiness, dry mouth, decreased appetite, and hyperexcitability (paradoxical in some cats). More serious side effects can occur, such as rapid heartbeat, difficulty breathing, severe sedation, and urinary retention.

Cautions · 12

When Benadryl should be used with caution or avoided

Some cats should not take Benadryl, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Benadryl.

glaucoma
urinary obstruction
hyperthyroidism
cardiovascular disease

Interactions · 13

Benadryl drug interactions

Benadryl can interact with other drugs. This list is not complete — always give your veterinarian a full list of your cat's medications and supplements.

CNS depressants

anticholinergic drugs

MAO inhibitors

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult cat at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

In an emergency, or after accidental ingestion or a suspected overdose
For pregnant or nursing pets
For very young or very old cats
For pets with liver disease, kidney disease, or another chronic illness
For pets taking several medications at once
When you are not sure of your cat's current, accurate weight
For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your cat had too much Benadryl, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

Call your veterinarian or the nearest emergency animal hospital.
ASPCA Animal Poison Control Center: (888) 426-4435
Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your cat experiences any of the following, contact your veterinarian or an emergency clinic immediately:

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

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

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.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your cat's weight by the lower, standard, and upper mg/kg values recorded for Benadryl. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses: allergies, itching, motion sickness, vaccine reactions
Recorded forms: tablet, liquid
Reference timing: every 8-12 hours; onset 30-60 minutes; duration 8-12 hours

Individual checks a calculator cannot perform

Confirm the diagnosis and the reason this medication is being considered.
Match the exact product, concentration, route, and whether a tablet may be split.
Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

glaucoma; urinary obstruction; hyperthyroidism; cardiovascular disease.

Recorded interactions

CNS depressants; anticholinergic drugs; MAO inhibitors.

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your cat's complete medication list before acting on a number.

Related · 08

Related medications for cats

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Plumb's Veterinary Drug Handbook — listed in this medication's source record.
Merck Veterinary Manual — listed in this medication's source record.
DailyMed label search for Diphenhydramine — check current product and formulation labels; some veterinary uses may be off-label.

Source names are shown at the record level; passage-level page and label citations are still being added. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

Sources cited: Plumb's Veterinary Drug Handbook
Merck Veterinary Manual
Calculator formula: Doses scale linearly from a standard basis of 2 mg per kg (0.91 mg per lb) of body weight, given every 8-12 hours. The calculator multiplies that basis by your cat's weight and shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner: Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status: Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

More on our methodology and editorial process — how we source, calculate, and review cats dosage data.

Safety · 10

More resources

Pet Medication Safety Hub — What's safe, what's dangerous, and emergency signs
How we calculate dosages — Our sources, math, and review process
Printable emergency checklist — One-page reference for your fridge or first aid kit