Yes, most healthy adult dogs can take plain Benadryl. The usual dose is 1 mg of diphenhydramine per pound of body weight (2.2 mg/kg), given every 8–12 hours. That is inside the Merck Veterinary Manual range of 2–4 mg/kg. A 25 lb dog gets one 25 mg tablet. Check with your vet first.
This calculator turns that dose into standard 25 mg tablets, 12.5 mg children's chewables and children's liquid (12.5 mg per 5 mL). It is general information, not veterinary advice. Human antihistamines are used "extra-label" in dogs, which under FDA rules is a decision for a veterinarian with a valid vet-client-patient relationship.
How to use this calculator
- Weigh your dog on a scale rather than guessing. Enter the weight in pounds or kilograms. If you need to convert, see our stone, pounds and kg converter.
- Leave the dose rate on Standard (1 mg/lb) unless your vet has told you to use the upper range.
- Read the dose in mg, then pick the product you have: tablets, chewables or liquid. Round tablets down to the nearest quarter.
- For dogs under 10 lb, use the children's liquid and an oral syringe. The calculator shows the volume in mL.
- Wait 8–12 hours between doses and give no more than three doses in 24 hours.
How the dose is calculated
Dose (mg) = weight (lb) × 1 mg/lb. One pound is 0.4536 kg, so 1 mg/lb equals 2.2 mg/kg, the bottom of the Merck Veterinary Manual range of 2–4 mg/kg by mouth every 8–12 hours. The upper-range option uses 4 mg/kg, about 1.8 mg/lb.
- 25 mg tablets = dose ÷ 25, rounded down to a quarter tablet (Benadryl Allergy Ultratab label: 25 mg diphenhydramine HCl).
- Chewables = dose ÷ 12.5 (Children's Benadryl Chewables label: 12.5 mg).
- Children's liquid (mL) = dose ÷ 12.5 × 5 (Children's Benadryl Allergy label: 12.5 mg per 5 mL).
- Maximum per day = three doses, the most you can give at 8-hour intervals.
Benadryl dosage chart for dogs
| Dog weight | Dose (mg) | 25 mg tablets | Children's liquid |
|---|---|---|---|
| 5 lb (2.3 kg) | 5 mg | 0.2 | 2 mL |
| 10 lb (4.5 kg) | 10 mg | 0.4 | 4 mL |
| 15 lb (6.8 kg) | 15 mg | 0.6 | 6 mL |
| 20 lb (9.1 kg) | 20 mg | 0.8 | 8 mL |
| 30 lb (13.6 kg) | 30 mg | 1.2 | 12 mL |
| 40 lb (18.1 kg) | 40 mg | 1.6 | 16 mL |
| 50 lb (22.7 kg) | 50 mg | 2 | 20 mL |
| 60 lb (27.2 kg) | 60 mg | 2.4 | 24 mL |
| 70 lb (31.8 kg) | 70 mg | 2.8 | 28 mL |
| 80 lb (36.3 kg) | 80 mg | 3.2 | 32 mL |
| 100 lb (45.4 kg) | 100 mg | 4 | 40 mL |
Worked examples
A 12 lb dog with a bee sting
12 lb × 1 mg/lb = 12 mg. That is 0.48 of a 25 mg tablet, so the liquid is the better choice: 4.8 mL of children's liquid. Vomiting, diarrhea, drooling or weakness after a sting is an emergency.
A 45 lb dog with itchy hives
45 lb × 1 mg/lb = 45 mg, or 1.8 tablets. Rounded down to the nearest quarter that is 1.75 tablets (43.75 mg). The Merck Veterinary Manual describes giving antihistamines for hives for 3–5 days to stop them coming back, usually alongside a steroid from your vet.
A 30 kg dog, upper range on vet advice
30 kg is 66.1 lb. At 4 mg/kg the dose is 120 mg (4.8 tablets); at the standard rate it would be 66.1 mg. Only use the upper range if your vet has prescribed it.
What Benadryl is used for in dogs
VCA Animal Hospitals lists allergic reactions, motion sickness and vomiting as uses of diphenhydramine in dogs, and notes it is also used as a mild sedative. The most common home use is for hives (urticaria): raised, dome-shaped bumps of about 0.5–3 cm, often on the head, legs and belly. The Merck Veterinary Manual lists insect bites, drug or vaccine reactions, food reactions and seasonal allergens as common triggers. Mild hives often settle within 12–48 hours.
Benadryl works less well for long-term itching. Merck notes that responses to antihistamines "vary considerably" and several may need to be tried. Dogs with ongoing allergic skin disease usually need a different treatment plan.
How to give Benadryl to a dog safely
- Check the label: the only active ingredient should be diphenhydramine HCl.
- Weigh your dog and use the calculator. Round down to the nearest practical tablet fraction.
- Small dogs (under 10 lb) are easier to dose accurately with the children's liquid and an oral syringe. Check that the liquid does not contain xylitol.
- Expect drowsiness. Less common side effects are dry mouth, urine retention, vomiting, diarrhea, loss of appetite or, occasionally, excitement.
- Store tablets at room temperature (59–86 °F), away from light and out of reach of pets.
Common mistakes to avoid
- Using a combination product. Decongestants such as pseudoephedrine and phenylephrine and pain relievers such as acetaminophen are dangerous for dogs (Merck Veterinary Manual).
- Missing xylitol in the ingredients. Some liquids, melts and chewables are sweetened with xylitol, which the ASPCA warns can cause a dangerous drop in blood sugar in dogs.
- Doubling up after a missed dose. VCA advises giving the missed dose when you remember and then carrying on as normal, never two doses at once.
- Mixing with other sedating drugs. Use caution with anticholinergic drugs, tricyclic antidepressants and other central nervous system depressants (VCA). Tell your vet about every medicine your dog takes.
When not to give Benadryl
Skip it and call your vet if your dog is a puppy, or has glaucoma, heart disease, high blood pressure, an overactive thyroid, prostate or bladder problems, is pregnant or nursing, or is on other medications. Merck lists heart disease, glaucoma and a tendency to urine retention as contraindications because of the drug's anticholinergic effects. Do not use this dose for cats.
When to see a vet right away
Benadryl is not a treatment for a severe allergic reaction. The Merck Veterinary Manual explains that in dogs the main organ affected by anaphylactic shock is the liver, so the warning signs are mostly gastrointestinal rather than breathing problems. Go to an emergency vet immediately if you see:
- sudden vomiting or diarrhea, heavy drooling, or weakness after a sting, bite, vaccine or new medicine;
- pale gums, cold legs, collapse, seizures or trouble breathing;
- swelling of the face or throat that is getting worse;
- signs of overdose such as agitation, tremors or seizures. Merck warns that antihistamine overdoses cause central nervous system over-excitement and can be fatal.
If you think your dog swallowed too much, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435, open 24/7 (a consultation fee may apply). Also see a vet if itching, hives or ear scratching lasts more than a few days.
Is your dog pregnant? Ask your vet before giving any medicine, and use the dog due date calculator to plan for the birth.
Frequently asked questions
Can you give a dog Benadryl?
Yes, plain Benadryl (diphenhydramine) is commonly used in dogs for mild allergies, itching, hives, insect bites and motion sickness, at about 1 mg per pound (2.2 mg/kg) every 8–12 hours. The Merck Veterinary Manual range is 2–4 mg/kg. Using a human antihistamine in a dog is 'extra-label' use, so check with your veterinarian first.
How much Benadryl can I give my dog?
The standard dose is 1 mg per pound (2.2 mg per kg), two to three times a day. A 25 lb dog gets about 25 mg, one standard 25 mg tablet. The veterinary range tops out at 4 mg/kg (about 1.8 mg/lb), which for a 25 lb dog is 45.4 mg.
How much Benadryl can I give a 10 lb dog?
About 10 mg, which is 4 mL of children's liquid (12.5 mg per 5 mL). That is less than half of a 25 mg tablet, so the liquid measured with an oral syringe is the more accurate option for small dogs.
How much Benadryl can I give a 50 lb dog?
About 50 mg, which is two 25 mg tablets, every 8 to 12 hours. The upper end of the Merck range (4 mg/kg) would be 90.7 mg, and should only be used if your vet tells you to.
How long does Benadryl take to work in dogs?
VCA Animal Hospitals says it usually takes effect within 1 to 2 hours. It is short-acting, which is why it is given every 8–12 hours, and it should wear off within 24 hours (longer in dogs with liver or kidney disease).
Which Benadryl is safe for dogs?
Only products whose single active ingredient is diphenhydramine. Avoid 'Benadryl-D', cold and sinus formulas with pseudoephedrine or phenylephrine, anything with acetaminophen, and any liquid or dissolving tablet sweetened with xylitol, which is toxic to dogs.
How often can I give my dog Benadryl for itching?
Every 8 to 12 hours, no more than three times in 24 hours. For hives the Merck Veterinary Manual describes a 3–5 day course. If itching lasts more than a few days, see a vet, because ongoing itch is usually allergic skin disease, fleas or infection that needs a different treatment.
What if I miss a dose or give too much?
If you miss a dose, give it when you remember and continue the normal schedule, but never give two doses at once (VCA). An overdose can cause over-excitement, tremors or seizures and can be fatal; call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 (24/7, a fee may apply).
Can I give my cat the same Benadryl dose?
No. This calculator is for dogs only. Cats are more prone to excitement on diphenhydramine, and the Merck Veterinary Manual advises avoiding it for hives in cats. Ask your vet for a cat-specific plan.
Sources & method
- Merck Veterinary Manual — Antihistamine dosages (diphenhydramine 2–4 mg/kg q8–12h)
- Merck Veterinary Manual — Urticaria (hives) in animals
- Merck Veterinary Manual — Antihistamines: side effects and contraindications
- Merck Veterinary Manual (Pet Owner) — Anaphylactic reactions in dogs
- VCA Animal Hospitals — Diphenhydramine
- Merck Veterinary Manual — Poisoning from human over-the-counter drugs
- ASPCA — Updated safety warning on xylitol
- ASPCA — Animal Poison Control Center
- DailyMed — Children's Benadryl Allergy liquid (12.5 mg/5 mL)
- DailyMed — Children's Benadryl Chewables (12.5 mg)
- DailyMed — Benadryl Allergy Ultratab (25 mg)
- FDA — Extra-label drug use in animals
Results are estimates for general information. Found an error? It helps everyone — see our methodology.