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Medication details

  • Medication type: Antihistamine
  • Form: Liquid, Capsule, Pill, Tablet, Injection
  • Prescription required? No
  • FDA approved? Benadryl, the name-brand drug, is not FDA-approved for veterinary use. Diphenhydramine, the generic compound, is approved in dogs in both veterinary and human formulations.
  • Brand names: Vetadryl, Calmatrol
  • Common names: Diphenhydramine hydrochloride
  • Available dosages: 10-50 mg
  • Warning: Diphenhydramine and Benadryl can be purchased as an over-the-counter drug, but should be given only under the direction of a veterinarian.

Dogs, like humans, experience allergies or allergic reactions. When this occurs, one method of relieving itchiness is using antihistamines. Humans use antihistamines to help with seasonal allergies, known allergic reactions, or reactions to specific exposures such as bug bites and poison ivy. 

Benadryl is one of the most common and well-known antihistamines. While it is safe in dogs, it is not FDA approved for use in animals. 

Diphenhydramine, the active ingredient in Benadryl is FDA approved and there are veterinary formulations specifically for our furry friends. 

What is Benadryl? 

Benadryl is a brand-name antihistamine used for allergy and itch relief that contains the active ingredient diphenhydramine. Discovered in 1943 by George Rieveschl, diphenhydramine became the first FDA approved antihistamine. 

Histamines are compounds released by the immune system in response to specific triggers. Most of the time these triggers are common contaminants in the environment such as dust, pollen, dander, or grass. When histamines are released by the body, they cause itching (pruritus). Histamine release is a natural response, but when it becomes excessive—as is the case for allergic reactions—medical intervention may be necessary.  

As an antihistamine, diphenhydramine prevents the release of histamine and therefore mediates itching and allergies. In humans it can also be used for insomnia, tremors, and nausea. 

Benadryl is available over the counter for pet parents to purchase but should only be used under the direction of a veterinarian. Veterinarians can also prescribe the dog form of Benadryl, Vetadryl, which is the FDA approved form of diphenhydramine for dogs. It’s always safer to receive an initial dosage and frequency from your veterinarian. 

Is Benadryl Safe for Dogs? 

Benadryl tablets in packaging

Benadryl is safe for dogs. The active ingredient, diphenhydramine, is used in veterinary formulations that are FDA approved. Veterinarians may recommend Benadryl to their clients whose pets have allergic reactions to vaccines or other medications. In this case, pet parents are advised to administer Benadryl at a determined dose a few hours prior to their appointment. 

Benadryl is safe for dogs at all life stages. The dosage will need to be adjusted according to your dog’s weight. It is best to consult with a veterinarian to determine a dosage for your pet and to discuss why you would like to administer Benadryl to your dog. 

Benadryl can be given to puppies and may be given more commonly to puppies than dogs in other life stages. Puppies receive vaccinations early in life and can have a reaction to these vaccines. To mediate vaccine reactions, veterinarians often recommend administering Benadryl 2-4 hours before the vaccine appointment to prevent reactions such as hives or swelling of the face. 

What is Benadryl Used For in Dogs? 

Dog scratching in yard

Your vet may recommend Benadryl to your dog for allergies and itchy skin. Benadryl is more effective for the prevention of allergic reactions than treating reactions after they have started. When there is a common, single trigger to your dog’s allergies it is better to give him a dose of Benadryl before he encounters the allergen rather than after the exposure. Nonetheless, Benadryl can still help with decreasing the side effects of an allergic reaction. 

A common side effect of Benadryl is drowsiness, so it may also be used to temporarily calm anxious dogs. 

Typically, Benadryl is not used for dogs with chronic itchy skin. It can be helpful for early or mild cases, but there are prescription drugs that have been shown to be more effective. Other medications such as Apoquel or prednisone are prescribed with dogs with chronic allergies or itchiness. 

In the veterinary clinic, your dog may receive Benadryl or diphenhydramine (common name) before receiving certain medications, vaccines, or a blood transfusion as these are well-known to cause hypersensitivity reactions. 

Types of Benadryl for Dogs 

Benadryl can be given orally, topically, or as an injection in the muscle (intramuscularly). Intravenous administration of Benadryl can cause seizures and is not used. 

Pet parents most commonly give Benadryl in tablet form by mouth. 

It is best to stick with the generic diphenhydramine to avoid other ingredients that may have adverse effects in your pet. Some antihistamines are combined with decongestants or acetaminophen which can cause toxicity in dogs at lower doses. 

Benadryl Side Effects in Dogs 

Similar to other drugs, Benadryl can have side effects in dogs. These include: 

  • Drowsiness 
  • Seizures 
  • Nausea/Vomiting 
  • Diarrhea 
  • Dry eye 

If you are concerned about any side effects, make sure to talk to you veterinarian. He or she may suggest a different dosage or transition your dog to a different antihistamine medication. 

Benadryl Dosage for Dogs 

Dog with allergic reaction

If you are concerned about your dog having an allergic reaction and would like to give him Benadryl it is best to consult your veterinarian for the correct dosing information. Your veterinarian may recommend a visit to the clinic to perform a physical exam on your dog to be sure that he is having an allergic reaction that Benadryl can help with and not suffering from a more serious condition. 

If your dog experiences seasonal allergies, your vet may recommend administering Benadryl on a regular basis. Some dogs may even take Benadryl once daily as a long-term therapy to mild allergies. Usually, these dogs receive Benadryl or diphenhydramine once daily. 

Although Benadryl is a safe drug, overdosing is possible. Signs to look for in your pet if you suspect at overdose are: 

  • Tremors
  • Disorientation 
  • Slow breathing 
  • Urinary retention (lack of urination) 

If you do suspect an overdose, you should call your veterinarian immediately and take in the packaging for the medication that was administered. 

Price of Benadryl for Dogs 

Benadryl tablets are about 20 cents per pill. The common name or generic drug, diphenhydramine will be less than half the price. Both are effective and the veterinary formulation, Vetadryl is the safest because it is FDA approved for use in pets. 

Some formulations of Benadryl, such as the children’s chewables or syrup, may contain substances that are toxic to dogs or increase the chances of side effects. 

Benadryl Storage Instructions 

Benadryl should be kept in its original container, tightly closed, and away from excess heat and moisture. The container or packaging will indicate the expiration and it should not be given past its expiration date. Never give your dog expired medication. 

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