Dogs are curious and energetic, so it’s inevitable that some of them will wind up in some sticky situations. From running through some poison ivy to getting stung by a bee, there are plenty of problems that can lead to your dog feeling itchy, uncomfortable, and swollen from an allergic reaction.  Your dog doesn’t need to suffer, though. With a vet’s guidance, you can use diphenhydramine (Benadryl) to ease the worst of their allergy symptoms. Here’s how Benadryl can be given to dogs safely. 

Benadryl, or diphenhydramine, is an antihistamine that helps relieve the symptoms of allergies in both humans and animals. It can also be used to relieve the symptoms of motion sickness if a dog needs to be transported long distances. For most dogs, the appropriate dosage of Benadryl is perfectly safe. It will begin to reduce symptoms like skin rashes in about an hour.  Getting the dosage right is important because most Benadryl tablets are intended for humans. Some dogs can be quite small, so they need less Benadryl than a person. Dogs also metabolize Benadryl differently, so it’s not a good idea to rely on human dosing guidelines. 


Benadryl is the brand name for the active ingredient diphenhydramine HCl. Diphenhydramine is a first-generation ethanolamine-derivative antihistamine, which is the scientific way of classifying antihistamines that can cross the blood-brain barrier – making them very effective but also increasing risks of adverse side effects. While Benadryl is not yet FDA-approved for veterinary use, it is considered safe for use in dogs and cats and is commonly used in veterinary practices across the U.S.

Diphenhydramine works by blocking the receptors that receive histamines in the body. This relieves many of the symptoms associated with allergies, like itching, sneezing, and hives. The body still produces histamines, but the receptor antagonist blocks the receptors from registering the histamines.

Features of Diphenhydramine For Dogs

Diphenhydramine is given by mouth in the form of a tablet, capsule, oral liquid, or liquid injection. The oral formulations can be given with or without food. If your pet vomits after dosing on an empty stomach, give future doses with food or a treat. The liquid has a bad taste to cats, and administration by mouth may be difficult. The injection is typically given in the hospital, either in the vein, muscle, or under the skin.

This medication will take effect quickly, in about 1 to 2 hours, and improvement in clinical signs should follow. If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Benadryl Dosage For Dogs

The general dosage guideline for dogs is 1mg of Benadryl for every pound of body weight. However, you must always consult your veterinarian, as there are a number of factors that can change this dosage recommendation. The average dosage included in one tablet is 25mg, so a 25-pound dog should be given one tablet. But you must check the dosage on the package; don’t assume that every product will be the same.

Stick to the pill form, as the liquid form may contain alcohol, which is toxic for dogs. For small dogs, you may wish to use the children’s formula, which has less of the active ingredient and may be easier for you to measure out. The children’s formula of liquid Benadryl contains no alcohol. In most cases, it’s better to administer medication before exposure to allergens. Follow your vet’s guidelines, and if they recommend a regimen, stick to it for the duration of your vet’s advisement even if symptoms seem to disappear.

It’s important to strictly follow your vet’s guidelines. Symptoms of an overdose of Benadryl in dogs include:

  • Rapid heart rate
  • Dilated pupils
  • Agitation
  • Constipation
  • Seizures

Uses/benefits of Diphenhydramine For Dogs

Benadryl is typically recommended by vets for dogs who are suffering from mild or moderate allergy symptoms. These allergies could be caused from seasonal allergies, environmental allergies such as grass, food allergies, or allergies that are caused by insect bites or snakes bikes. Benadryl is commonly recommended for dogs who are sufferings from skin allergies and itchiness that is caused by this type of allergy reaction.

The most common symptoms that Benadryl can treat:

  • Itchy skin
  • Red or inflamed skin
  • Swelling and inflammation
  • Eye boogers or discharge buildup
  • Constant sneezing
  • Coughing or hacking
  • Runny nose or red eyes
  • Hives
  • Itchy or red ears


  • Individuals may react differently to antihistamines. The dose of diphenhydramine should be tailored to the individual animal.
  • Antihistamines should be used with caution in working dogs due to the sedative side effects.
  • Diphenhydramine should be used with caution in animals with prostatic hypertrophy, bladder neck obstruction, severe heart failure, angle closure glaucoma, pyeloduodenal obstruction,
  • Hyperthyroidism, seizure disorders and hypertension or allergic lung disease (COPD).
  • Older humans are more sensitive to side effects from antihistamines. A lower dose of diphenhydramine may be indicated in older animals.
  • High doses of antihistamines can cause birth defects in laboratory animals. Diphenhydramine is excreted in breast milk. It should be used only in pregnant or lactating animals if the benefits outweigh the risks.

Drug Interactions

  • Diphenhydramine may have an addictive effect when combined with other CNS depressant drugs, such as barbiturates and tranquilizers or when combined with other anticholinergic agents.
  • Diphenhydramine may enhance the effects of epinephrine.
  • Diphenhydramine may decrease the effects of heparin and warfarin.


  • Overdose with diphenhydramine can cause symptoms ranging from CNS stimulation to CNS depression.
  • The usual signs of mild overdose are sedation and clumsiness. Seizures, respiratory depression, coma and death can occur after a massive overdose.
  • In humans, phenytoin is the recommended treatment for seizures due to antihistamine overdose. Diazepam and barbiturates should be avoided.

Prices of Diphenhydramine For Dogs

$29.15 – $70.99

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