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The temptation to reach into our medicine cabinets to treat our pets can be dangerous. Humans and dogs react very differently to medications, which is why veterinarians caution dog owners against making independent decisions about how to medicate their animals. However, some human medications are safe for use with dogs, as long as they are used appropriately.

Veterinarians use diphenhydramine, commonly known by the brand name Benadryl, for dogs on a regular basis to treat allergies, travel anxiety, and motion sickness. While you should always consult with your veterinarian before giving your dog a human medication, here is what you need to know about using Benadryl for dogs.

What Is Benadryl?

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.

What Does Benadryl Treat in Dogs?

Benadryl is a great medication for use in dogs with mild-to-moderate allergies. Seasonal allergies, food allergies, environmental allergies, and allergic reactions to snake and insect bites all respond to Benadryl in most cases. Benadryl is commonly used to treat itchiness in dogs caused by skin allergies, and it also reduces many of the other symptoms of allergies, including:

  • Hives
  • Swelling and inflammation
  • Redness
  • Runny nose and eyes
  • Coughing
  • Sneezing
  • Anaphylactic reaction

One of the side effects of Benadryl is drowsiness, which helps to calm anxious dogs. The Merck Veterinary Manual states that diphenhydramine may relieve symptoms of mild-to-moderate anxiety in pets associated with travel. It also may help relieve motion sickness. Although Benadryl may sometimes relieve anxiety, it’s best to talk to your veterinarian or an animal behaviorist to determine and treat what’s causing the anxiety.

Veterinarians prescribe Benadryl for dogs with mast cell tumors to help mitigate the effects of the massive histamine release caused by mast cell degranulation. Veterinarians sometimes prescribe diphenhydramine during heartworm treatment, as it helps reduce the risk of an allergic reaction to the heartworm treatment therapy. Benadryl makes an excellent addition to your pet first aid kit.

Bull Terrier rolling in the grass outdoors at sunset.

When to Ask Your Vet About Benadryl for Dogs

Before you reach for the Benadryl, consult your veterinarian about your dog’s symptoms. Allergy symptoms like itching and red eyes are also signs of more serious conditions. In some cases, giving your dog Benadryl can actually worsen your dog’s condition. Red, goopy eyes could be a symptom of allergies, or it could also be a sign of glaucoma or dry eye, which Benadryl will not help treat. Similarly, itching is frequently associated with allergies and other skin conditions. Your vet will also be able to tell you whether Benadryl will interact with other medications that your dog is taking.

Side Effects of Benadryl

There are side effects associated with using Benadryl for dogs that all dog owners should be aware of. Most side effects occur within the first hour of exposure, so monitor your dog carefully during this time.

If your dog has any of the following conditions, only use Benadryl after consulting your veterinarian:

Common side effects associated with using Benadryl for dogs include:

  • Drowsiness
  • Dry mouth
  • Urinary retention
  • Hypersalivation
  • Increased heart rate
  • Rapid breathing

Rare side effects include:

Benadryl Overdose

It’s possible to overdose on Benadryl. Signs of an overdose include hyper-excitability of the central nervous system, which can be fatal. Other warning signs to watch for are:

  • Rapid heartbeat
  • Dilated pupils
  • Agitation
  • Constipation
  • Seizures

If you suspect your dog has overdosed on Benadryl, contact your veterinarian or emergency veterinary hospital immediately. Some dogs develop an allergic reaction to Benadryl. If your dog starts having symptoms of an allergic reaction, seek veterinary care immediately.

Dosage of Benadryl for Dogs

The best way to determine the correct Benadryl dosage for dogs is to consult your veterinarian. The Merck Veterinary Manual recommends administering 2-4 milligrams of Benadryl per kilogram of body weight, two to three times a day. However, this dosage can vary depending on your dog’s medical conditions.

Dr. Jerry Klein, AKC chief veterinary officer, warns that you should always consult with a veterinarian before giving Benadryl to a puppy because young puppies can be very sensitive to certain medications. The drug is also not recommended for pregnant or nursing dogs

Never use time-release capsules for dogs, as capsules are absorbed differently in dogs than in humans and may affect your dog’s dosage. They may also break open when chewed and deliver too much medication at one time, putting your dog at risk of an overdose.

It’s best to avoid using liquid Benadryl if it contains sodium, which can cause other side effects. Also avoid any form of Benadryl that contains alcohol.

Children’s Benadryl pills or tablets can be used safely if you ask your veterinarian for the appropriate dosage.

Is Benadryl Safe for Your Dog?

Benadryl is a relatively safe and effective medication for dogs when used according to the instructions of a veterinarian. As with any new medication, always observe your dog closely after administration to make sure there aren’t any adverse reactions. If you have any further questions about Benadryl for dogs, contact your veterinarian for more information. And remember to keep all medicines out of reach of your curious canine pal.

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