Benadryl (Diphenhydramine) Dosage Calculator for Cats by Weight
Dose ranges on this page are published veterinary references for education only. Your veterinarian's prescribed dose always wins. When in doubt, call your vet first.
Unlike in dogs, diphenhydramine (Benadryl) is not a routine go-to antihistamine for cats. Veterinary references that do list a feline dose use a conservative range of roughly 0.5–1 mg per kg of body weight, given every 12 hours.
The calculator below shows that conservative range for your cat's weight. Because cats are small and sensitive to antihistamines, confirm the dose with your veterinarian before giving anything — especially for kittens, seniors, or cats on other medications.
Dose calculator
Dosage chart by weight
| Cat weight | Dose range per dose |
|---|---|
| 5 lb | 1.1–2.3 mg |
| 8 lb | 1.8–3.6 mg |
| 10 lb | 2.3–4.5 mg |
| 12 lb | 2.7–5.4 mg |
| 15 lb | 3.4–6.8 mg |
| 18 lb | 4.1–8.2 mg |
| 20 lb | 4.5–9.1 mg |
Chart uses the same conservative range as the calculator (0.5–1 mg per kg of body weight (conservative feline range)). Always confirm with your veterinarian.
Common formulations
- Standard tablets — 25 mg tablets
Usually needs splitting — confirm with your vet - Children's liquid (12.5 mg / 5 mL) — 12.5 mg / 5 mL
Must not contain xylitol or alcohol
Use the calculator above to convert any of these sizes into an amount for your pet's weight.
How often to give it
Every 12 hours. 0.5–1 mg per kg of body weight (conservative feline range).
Keep a single dose at or below about 12.5 mg per cat unless your veterinarian directs otherwise.
Common veterinary uses
- Occasional mild itching (vet-directed)
- Mild allergic signs (vet-directed)
- Motion sickness (vet-directed — other options are usually preferred)
Safety warnings
Possible side effects
- Sedation or sleepiness
- Dry mouth
- Rarely: paradoxical excitement or hyperactivity
- Drooling with liquid formulations (taste)
- Use PLAIN diphenhydramine only. Never use Benadryl-D (pseudoephedrine is dangerous for cats).
- Avoid products with acetaminophen — toxic to cats even in small amounts.
- Check liquid inactive ingredients for xylitol or alcohol.
Do not use (or ask your vet first)
- Cats with glaucoma or urinary obstruction, unless your vet directs otherwise
- Cats with heart disease or high blood pressure
- Pregnant or nursing cats — ask your vet first
When to see a veterinarian
- Any breathing difficulty or facial swelling — emergency vet immediately
- Vomiting, extreme lethargy, or loss of appetite after dosing
- Tremors, agitation, or collapse
- You are unsure about the dose — with cats, guessing is not worth the risk
Frequently asked questions
Can cats take Benadryl?
It is occasionally used in cats under veterinary direction, but it is far less routine than in dogs. Published feline references use a conservative 0.5–1 mg/kg every 12 hours. Call your vet before dosing your cat.
How much Benadryl for a 10 lb cat?
10 lb is about 4.5 kg. At 0.5–1 mg/kg, the conservative range is roughly 2–4.5 mg every 12 hours — a small fraction of a 25 mg tablet. This is why veterinary guidance matters for cats.
Why is Benadryl less common for cats?
Cats respond less predictably to first-generation antihistamines, dosing margins are tighter in small animals, and other options are often preferred. Your vet can advise what fits your cat's situation.
What are signs of Benadryl overdose in cats?
Extreme sedation or paradoxical hyperactivity, tremors, rapid heart rate, or seizures. Contact your vet or poison control immediately if you suspect an overdose.
Sources
- Cedarview Veterinary Clinic — Antihistamine Dosing Chart (PDF)
- Vetnique — Benadryl for Dogs (dosing background)
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Dose ranges on this page are published veterinary references for education only. Your veterinarian's prescribed dose always wins. When in doubt, call your vet first.