How to Use Antihistamines for Dogs

How to Use Antihistamines for Dogs

Just like people, dogs can sometimes have allergies that flare up, or they have to deal with things like pesky insect bites and stings while outside, which can also cause an allergic reaction. When that’s the case, dog owners just want to make their pet feel better, as quickly as possible. This is why they often consider using antihistamines for dogs. But just how do they work? Are they safe? And do you need a prescription, or are over-the-counter antihistamines available?

What Causes Allergies in Dogs


There are many things that dogs can be allergic to and just like people, different dogs will have different allergies. If a dog is to develop an allergy, it’s likely going to be between the ages of one and three, but some dogs develop allergies when they’re as old as six as well. While most allergies are airborne, which means your dog inhales them before showing symptoms, there are other types of allergies, such as bee stings and flea bites that can also cause an allergy.

Environmental factors such as pollen, hay, and grass can cause allergies in dogs and symptoms will be present when the dog is exposed to them. This is an easy type of allergy to diagnose and treat, as a simple blood test at your veterinarian’s office will determine if an allergy is present.

If the test comes back as positive, your vet can offer an allergy shot to help treat the symptoms, or you can choose to give your pet antihistamines.

Certain food can also cause an allergic reaction in dogs, but this allergy is much more difficult to pinpoint and treat. The symptoms of this allergy can often show up as a chronic ear infection, or even feet that are constantly red instead of the usual itching and sneezing. Unfortunately, blood tests are also an ineffective way to diagnose a food allergy in dogs, so the only real treatment is an elimination diet, which could take anywhere from eight to twelve weeks.

Fleas and dust mites are the last of the most common dog allergies, and the allergy is more than just the mild itching that comes with these infestations. When a dog is actually allergic to the fleas, they are allergic to the saliva of the insect and so experience excessive itching that they can suffer from even with just one or two of the critters on their body.

Flea allergies are typically treated with topical treatments that are applied directly to the skin, but if your pet is really suffering your vet may also recommend an antihistamine that will keep them comfortable until the fleas are no longer present.

What Antihistamines for Dogs Are Available?

The main irritating agent of allergies is histamine, a chemical that is formed inside the body after the allergen is inhaled and attaches to tissue mast cells in the skin. It makes sense that to deal with the histamine, you need an antihistamine.

There are many antihistamines on that market that are all safe, and may be appropriate for your dog.

Benadryl for DogsChlorpheniramine is one that comes in a tablet form that is either time-released, or given to your dog three times a day. While Chlorpheniramine is a brand name, you may also choose to use a generic antihistamine such as Clemastine, formerly known as “Tavist,” which is given less often, every 12 hours. While both of these antihistamines are very effective, most dog owners settle for Benadryl when looking to treat their dog’s allergy symptoms.

Benadryl is very effective at stopping many symptoms of the most common allergies including swelling and excessive itching. The typical dosage to use is 1 milligram for every pound of your dog’s weight, but you definitely want to speak to a vet before administering any type of medication to your dog.

When looking at Benadryl specifically, it’s important to look at the label and ensure that diphenhydramine is the only active ingredient and that the product is Benadryl for allergies only. Other products such as Benadryl Allergy Plus Congestion will contain other active ingredients that could be harmful to your pet. Also be careful of giving your dog the liquid form of Benadryl, as this could also contain other ingredients such as alcohol, which could also be hurt your dog and hinder a speedy recovery.

Common Side Effects of Antihistamines in Dogs

Just like when people use them, giving your dog antihistamines could result in some side effects.

While typically most dogs will only experience the drowsiness and fatigue that is almost notorious with these medications, there are some others to look for.

Some of these side effects include:

  • Dry mouth
  • Dizziness
  • Nausea and vomiting
  • Trouble urinating
  • Blurry vision
  • Confusion
  • Excitement
  • Excessive barking
  • Excessive hunger or thirst
  • Diarrhea
  • Loss of appetite
  • Increased or decreased blood pressure

If any of these symptoms appear, or if you notice any other symptoms that are unusual or concerning about your dog, make sure that you speak to your veterinarian right away.

It’s important to remember that antihistamines will not cure your dog of their allergies, they will only suppress the symptoms and make your pet more comfortable until the allergen is no longer an irritant to them. Using antihistamines is not always as easy as just picking some up at the drugstore, either. While one type may work for one dog, it might not work for another, so even when you’re dealing with environmental factors, it could still take weeks to find the right product for your pet.

How to introduce antihistamines to your dog

Determining if an antihistamine is working in your dog can be tricky. Not only may a specific antihistamine not work for your dog, but an antihistamine can also appear to falsely work.

For instance, you could start giving your dog an antihistamine and the allergy symptoms disappear, causing you to think that the antihistamine worked. However another reason, such as the fact that pollen season is over, could be the real reason for your dog’s suffering to come to an end. Because of this, there is a certain process to follow when introducing antihistamines to your dog.

Start by introducing the antihistamine at a time when your dog’s allergies seem to be at their worst. Most dog owners will find that this time is during the spring and the summer. If you’re unsure, ask your vet to check your dog’s medical history and look for patterns in the times that your dog’s allergies were their worst.

Once your dog has been on an antihistamine for about a month and their condition seems to have improved, stop giving it to them temporarily. If their symptoms come back, it’s a good bet that the allergies are still present but that the medication is working. If their symptoms don’t come back however, there was likely another cause for the cessation of symptoms and you may have to dig further to find out what that was.

Once your dog has been responding well to a certain antihistamine, speak to your vet about trying a different type of antihistamine. You never know, you could find one that’s even better at treating your dog’s symptoms than the one you’re currently using.

When using antihistamines for dogs, no matter what the cause of their allergy or what type you’re giving to them, it’s important to remember that the antihistamine is not a cure, but only a way to suppress the symptoms and make your pet more comfortable. And while there are many effective antihistamines available, you must always speak to a vet before administering any type of medication to your pet.



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Kate Elliott

Kate Elliott

Kate Elliott has been a freelance content writer for the past 8 years, and has written creatively her entire life. In addition to her online work, she has written a fiction novel, as well as had poetry published in the “Songs of the Heart” collection. A lover of animals since she was young, she’s also always had a dog by her side. Currently her best friend is a 13-year-old German Shepherd named Chewy.

Kate Elliott

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