Benadryl, known scientifically as Diphenhydramine, is a household name when it comes to managing allergies. But when our canine companions start sneezing, itching, or showing signs of anxiety, many pet owners wonder: is what works for us, safe for them?

One question, in particular, seems to crop up frequently in the minds of dog owners and in online pet forums: “Can Benadryl cause constipation in dogs?

Benadryl Side Effect: Can Benadryl Cause Constipation In Dogs?

This isn’t just a matter of comfort for your furry friend—it’s an issue that could have broader health implications. This blog post will explore the effects of Benadryl in dogs, focusing on its potential to cause constipation, and provide you with a comprehensive understanding based on veterinary insights and scientific research.

What is Benadryl and How is it Used in Dogs?

Benadryl is a brand name for the antihistamine Diphenhydramine. It’s widely used by humans to alleviate symptoms of allergies, such as runny nose, sneezing, and hives.

In dogs, Benadryl is often recommended by veterinarians to treat similar allergic reactions, including itching, swelling, and other allergy symptoms. It can also be used to help manage anxiety and motion sickness during car rides or flights.


The active ingredient, Diphenhydramine, works by blocking the H1 receptors in the body. These receptors are involved in the allergic response and, when stimulated, lead to the symptoms we associate with allergies. By blocking these receptors, Benadryl helps to reduce or eliminate these symptoms.

You may like reading about: Can Benadryl Treat Vertigo In Dogs?

Can Benadryl Cause Constipation in Dogs?

When it comes to the question, “Can Benadryl cause constipation in dogs?” the answer is not straightforward.


While constipation is not typically listed as a common side effect of Benadryl in dogs, any medication has the potential to cause gastrointestinal upset in some pets.

Antihistamines like Benadryl can have a drying effect on the body. They reduce bodily secretions, which can lead to drier stool and, potentially, constipation.

However, it’s important to note that not all dogs will experience this side effect, and it can be influenced by factors such as dosage, frequency of administration, and the individual dog’s health and sensitivities.

If you notice that your dog is straining to defecate, passing hard or dry stools, or not passing stools at all after taking Benadryl, it’s important to consult with your veterinarian. They can provide guidance and determine whether the medication is the likely cause.

Other Common Side Effects of Benadryl in Dogs

Besides the potential for constipation, Benadryl can cause other side effects in dogs. The most commonly observed side effect is drowsiness. This is because, in addition to blocking H1 receptors, Diphenhydramine also has a mild sedative effect on the central nervous system.


Other possible side effects include:

  • Dry mouth, which can lead to increased thirst.
  • Urinary retention, which is the inability to fully empty the bladder.
  • Increased heart rate.
  • Rapid breathing.
  • Less commonly, dogs may experience diarrhea, vomiting, or a lack of appetite.

It’s crucial to monitor your dog for any changes in behavior or physical condition after administering Benadryl. If you notice any adverse reactions, contact your vet immediately.

You may like reading about: Good Sources Of Fiber For Dogs

Safe Dosage and Precautions

The safe dosage of Benadryl for dogs typically ranges from 1 mg per pound of body weight to 2 mg per pound, administered 2-3 times a day. However, this is a general guideline, and the appropriate dose can vary based on your dog’s specific needs and health status.

It’s imperative to consult your veterinarian before giving Benadryl to your dog. They can provide an accurate dosage and ensure that it’s safe for your pet, particularly if your dog is on other medications or has pre-existing health conditions.

Warning: Certain forms of Benadryl formulated for humans contain additives like xylitol, which is toxic to dogs.

Always check the ingredients list and use a product that is vet-approved or specifically formulated for pets.

Read about: Can Dogs Get Addicted To Diphenhydramine?

Alternatives to Benadryl for Dogs with Allergies

If Benadryl is not suitable for your dog or if you’re looking for alternative solutions, there are other options available. Depending on the severity and nature of your dog’s allergies, your vet might recommend:

You may like to read about: Benadryl & Acepromazine Together


Understanding the side effects of any medication, including Benadryl, is crucial when it comes to the health and well-being of our canine companions. While constipation is not a widely recognized side effect of Benadryl in dogs, it is a potential risk, especially given the drying properties of antihistamines.

Remember, always consult with your veterinarian before administering any new medication to your pet. By being a responsible and informed pet owner, you can ensure your furry friend remains healthy and happy.

You may like reading about: Do Antibiotics Cause Constipation In Dogs?

Frequently Asked Questions:

What is the recommended dose of Benadryl for dogs?

The general guideline is 1 mg to 2 mg of Benadryl per pound of body weight, administered 2-3 times a day. However, always consult your veterinarian for the precise dosage suitable for your dog.

How quickly does Benadryl take effect in dogs?

Benadryl typically begins to take effect within 30 minutes of administration, with peak effects occurring 1-3 hours after dosing.

Are there any breeds of dogs that should not take Benadryl?

Certain breeds with pre-existing conditions, such as glaucoma, high blood pressure, or heart disease, may not be suitable candidates for Benadryl. Breeds prone to these conditions should be evaluated by a veterinarian before using Benadryl.

What should I do if I think my dog is constipated after taking Benadryl?

If your dog shows signs of constipation after taking Benadryl, it’s important to consult your veterinarian. They can provide guidance on whether the medication is the cause and suggest appropriate treatment.

Can I give my dog Benadryl for long-term allergy treatment?

Benadryl is typically used for short-term relief of allergy symptoms. For long-term management, it’s best to consult your veterinarian for alternative treatments that are safe for prolonged use.

Doctor Xeeshan

Doctor Xeeshan

I am Doctor Xeeshan, located in Lahore, Punjab, Pakistan. In this blog, I am providing authentic information about dog breeds, diseases, medications, etc.


Leave a Reply

Avatar placeholder

Your email address will not be published. Required fields are marked *

close X

Try The Best Rated Dog Food On Amazon

Ancient grains like grain sorghum, millet, quinoa and chia seed are naturally high in fiber and rich in protein. Unchanged for thousands of years, different grains provide various nutrients such as vitamins, minerals, antioxidants and omega fatty acids.