Every dog owner knows the anxiety that comes with seeing their furry friend in discomfort. Whether it’s a reaction to an allergen or anxiety during a thunderstorm, the urge to provide relief is strong. This is where Benadryl, a common antihistamine used in humans, often comes into play.

Does Benadryl Cause Increased Heart Rate In Dogs?

But as responsible pet owners, it’s crucial to understand the effects of human medications on our canine companions. A particularly pressing question is, “Does Benadryl cause an increased heart rate in dogs?

This article delves into this question, providing insights into the use of Benadryl in veterinary care, its effects on dogs, and crucial safety guidelines.

What is Benadryl and How is it Used in Dogs?

Definition and Composition

Benadryl, known generically as diphenhydramine, is an antihistamine primarily used to treat allergies and allergic reactions in humans. Its primary function is to block histamine, a substance in the body that triggers allergic symptoms.

Common Uses in Dogs


In veterinary medicine, Benadryl is often used for similar purposes. It’s commonly administered to dogs for allergies, insect stings, motion sickness, and as a mild sedative. However, unlike in humans, the use of Benadryl in dogs should always be under veterinary guidance.

Dosage and Administration

The dosage of Benadryl for dogs typically depends on the dog’s weight. It’s crucial to never administer human medications to dogs without consulting a veterinarian, as the dosage and frequency can vary greatly.

The Effects of Benadryl on Dogs – Increased Heart Rate

Benadryl works by blocking histamine receptors in the body, effectively reducing symptoms like itching, sneezing, hives, swelling, redness, runny nose, and eyes, as well as coughing.

It’s important to note that Benadryl is not FDA-approved for veterinary use but is commonly used in veterinary practices across the U.S.​​.

Benadryl Affect On the Heart Rate


One notable side effect of Benadryl in dogs is drowsiness, which can calm anxious dogs. It also may help relieve symptoms of mild-to-moderate travel anxiety and motion sickness in pets. However, in terms of cardiovascular effects, increased heart rate is a less common but possible side effect of Benadryl in dogs.

This can be a concern, especially in dogs with pre-existing cardiovascular disease. Therefore, Benadryl should be used with caution in dogs with;

  • cardiovascular conditions
  • glaucoma
  • hypertension
  • hypothyroidism
  • seizure disorders
  • allergic lung disease
  • during pregnancy​​​​

Comparisons with Other Species

While Benadryl has similar effects in humans and dogs, such as drowsiness, the way it affects heart rate may vary.

In dogs, an increased heart rate is a less common side effect compared to other side effects like drowsiness or dry mouth.

This difference underscores the importance of considering species-specific responses when using medications like Benadryl.

Research and Veterinary Insights

Study Summaries

A study involving twelve healthy laboratory beagle dogs was conducted to compare the effects of oral diphenhydramine and cetirizine on cutaneous allergic reactions.

The study found that while cetirizine significantly reduced histamine and compound 48/80 global wheal scores and late-phase reactions, diphenhydramine did not show a significant inhibitory effect, despite achieving therapeutic plasma drug concentrations.

Importantly, no adverse effects or behavioral changes were observed during the study, indicating the safety of these medications in the tested conditions​​.

Expert Opinions

Veterinary professionals often consider Benadryl a safe and effective medication for treating allergies and anxiety in dogs when used in appropriate doses. However, they also advise caution, especially with long-term use, as the effectiveness of Benadryl can diminish over time.

In such cases, rotating through different antihistamines like cetirizine, loratadine, and chlorpheniramine is recommended.

Moreover, it’s crucial for pet owners to be aware of Benadryl’s side effects, including drowsiness, dry mouth, urinary retention, and less commonly, diarrhea, vomiting, loss of appetite, allergic reactions, and excitement​​​​​​​​.

Safety and Precautions

Safety Measures

When administering Benadryl, it’s vital to monitor your dog for any unusual symptoms. Stick to the prescribed dose and schedule, and never mix it with other medications without veterinary approval.

Warning Signs


Signs of a negative reaction to Benadryl can include;

  • excessive sedation
  • confusion
  • rapid heart rate
  • respiratory distress

If you observe any of these symptoms, contact your veterinarian immediately. For dogs that react poorly to Benadryl or for whom it’s not recommended, veterinarians can suggest alternative treatments or medications.


Can Benadryl cause an increased heart rate in all dogs?

Benadryl can cause an increased heart rate or breathing rate in some dogs, which may be a sign of an allergic reaction or overdose. This side effect, however, is not universal in all dogs and can vary based on individual factors.

Dogs may also experience an increased heart rate as a less dangerous side effect of Benadryl, but it is not common for all dogs to have this reaction.

What should I do if I notice an increased heart rate in my dog after giving Benadryl?

If you observe an increased heart rate in your dog after administering Benadryl, it is important to contact your veterinarian immediately. This could be a sign of an allergic reaction or an overdose. Symptoms typically show up within the first hour of dosing, so close monitoring during this period is crucial.

Are certain breeds more susceptible to this side effect?

Most dog breeds tolerate Benadryl well, but some breeds are more susceptible to its sedative effects. Specifically, brachycephalic breeds, such as Bulldogs and Pugs, which have short noses and flat faces, may be more prone to respiratory issues.

These issues can be exacerbated by Benadryl’s side effects. It is essential to consult with a vet before administering Benadryl to these breeds.

How quickly can Benadryl affect a dog’s heart rate?

If Benadryl is going to affect a dog’s heart rate, symptoms usually manifest within the first hour of dosing. It is important to monitor dogs closely during this period for any signs of adverse reactions.

Can long-term use of Benadryl impact a dog’s heart health?

It is generally advised to use any medication, including Benadryl, under the guidance of a veterinarian, especially for long-term use. Monitoring for any potential side effects or health changes is crucial in these situations.


In conclusion, while Benadryl is generally safe for dogs and not commonly associated with increased heart rate, individual reactions can vary. It’s imperative to follow veterinary guidance, monitor your dog closely after administration, and be aware of any adverse reactions. Always prioritize your pet’s health and safety and consult your veterinarian for the best course of action.

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.

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