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When Will Benadryl Hurt a Dog?



Reviewed By: Dr. Joel Robertson

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When it comes to dogs and Benadryl, many pet owners are unsure of when the medication will help or hurt their furry friends.

Benadryl is commonly prescribed by veterinarians as a treatment for allergies, motion sickness, and other conditions in both cats and dogs.

But how much should you give your dog and what side effects might occur?

This blog post will provide an overview of when Benadryl might hurt a dog and tips for safely administering the medication.

Key Takeaway

  • Benadryl can harm a dog if it’s given in excessive doses leading to toxicity, or if the dog has specific health conditions such as glaucoma, cardiovascular disease, or allergies to the medication itself.
  • Benadryl can be harmful to dogs with certain health conditions and can interact negatively with other medications, potentially worsening the dog’s condition.
  • Overdosing a dog with Benadryl can lead to serious health risks including rapid heartbeat, dilated pupils, agitated behavior, slowed breathing, tremors or seizures, and in severe cases, it can be fatal.

When Will Benadryl Hurt a Dog?

When Will Benadryl Hurt a Dog

Benadryl will hurt a dog if it’s administered in an inappropriate dosage, resulting in an overdose, or if the dog has certain health conditions that make it unsafe for them to consume this medication.

Benadryl, while generally safe for dogs in the correct dosage, can lead to toxicity if consumed in large amounts.

This overconsumption of the antihistamine ingredients can have harmful effects on a dog’s body. It’s important to understand that the dosage for dogs is significantly different from that for humans.

Typically, the dosage is calculated as 1mg per pound of the dog’s weight. Overdosing on Benadryl can result in symptoms such as constipation, sedation, urinary retention, vomiting, increased heart rate, diarrhea, and loss of appetite.

In some extreme cases, overdosing can even be fatal. Furthermore, some dogs may have underlying health conditions that can exacerbate the side effects of Benadryl or lead to negative interactions with other medications they are taking.

Therefore, it’s crucial to always consult with a veterinarian before administering any human medication, including Benadryl, to your pet. They can provide accurate dosage instructions and monitor your pet for any adverse reactions.

What Are the Risks of Overdosing My Dog with Benadryl?

The risks of overdosing a dog with Benadryl include serious health issues such as rapid heartbeat, dilated pupils, agitated behavior, slowed breathing, tremors or seizures, and even coma or death in severe cases.

Rapid Heartbeat

An overdose of Benadryl can cause your dog’s heart to beat rapidly. This is because the drug stimulates the central nervous system when consumed in high amounts. A rapid heartbeat can lead to cardiac arrhythmias, which could be life-threatening if left untreated.

Dilated Pupils

Another sign of Benadryl overdose in dogs is dilated pupils. This symptom might be accompanied by disorientation or agitation, indicating that the drug is affecting the dog’s nervous system. It’s important to seek immediate veterinary attention if you notice these signs.

Agitated Behavior

Overdosing on Benadryl can lead to changes in a dog’s behavior. They may become hyperactive or excessively agitated due to the overstimulation of their central nervous system. This could lead to accidents or injuries as the dog may not be able to control its movements properly.

Slowed Breathing

High doses of Benadryl can slow down a dog’s respiratory rate, potentially leading to respiratory failure. This is a critical condition that requires immediate veterinary intervention.

Tremors or Seizures

Tremors or seizures are serious signs of a Benadryl overdose. They occur due to the drug’s impact on the dog’s nervous system. If your dog experiences tremors or seizures after taking Benadryl, it’s crucial to get them to a vet as soon as possible.

Coma or Death

In severe cases, a Benadryl overdose can lead to a comatose state or even death. This is often the result of respiratory failure or cardiac complications. It underscores the importance of using the correct dosage and consulting with a vet before administering Benadryl to your dog.

Can Benadryl Be Harmful to Dogs with Certain Health Conditions?

Sure, here’s a table that outlines how Benadryl can be harmful to dogs with certain health conditions.

Health ConditionHow Benadryl Can Be Harmful
GlaucomaBenadryl can worsen the symptoms of glaucoma by causing an increase in intraocular pressure. This could lead to further vision loss.
Cardiovascular DiseaseBenadryl can cause changes in heart rate and blood pressure, which can be particularly dangerous for dogs with pre-existing heart conditions.
Allergies to BenadrylSome dogs may be allergic to Benadryl itself. This can lead to severe allergic reactions including difficulty breathing, hives, swelling, or other symptoms.
Prostate HypertrophyBenadryl can exacerbate the symptoms of prostate hypertrophy, making it difficult for male dogs to urinate.
Seizure DisordersIn dogs with seizure disorders, Benadryl might potentially trigger a seizure.
Pregnant DogsBenadryl might affect the health of pregnant dogs and their unborn puppies, potentially leading to complications.

Is It Dangerous to Give Benadryl to Puppies or Small Breed Dogs?

Giving Benadryl to puppies or small breed dogs is not inherently dangerous, but it must be done with caution due to their size and sensitivity to medications.

Benadryl, a common antihistamine, is generally well-tolerated in dogs, including puppies and small breeds. However, the key to its safe use lies in the correct dosage.

The dosage should always be determined based on the dog’s weight, and it’s especially important to get this right with smaller dogs and puppies due to their size.

Overdosing can lead to serious health issues such as rapid heartbeat, dilated pupils, agitated behavior, slowed breathing, and even tremors or seizures.

Are There Any Known Allergic Reactions in Dogs to Benadryl?

Yes, while rare, dogs can have allergic reactions to Benadryl, which may manifest as swelling of the face and tongue, vomiting, diarrhea, an upset stomach, skin rashes, and elevated heart rate.

Swelling of Face and Tongue

One potential allergic reaction to Benadryl in dogs is facial swelling, especially around the mouth and tongue. This can be a serious issue as it may lead to difficulty breathing if not addressed immediately.

Vomiting and Diarrhea

An allergic reaction to Benadryl can also cause gastrointestinal issues in dogs. These can include vomiting and diarrhea, which can lead to dehydration and electrolyte imbalances if severe or prolonged.

Upset Stomach

Dogs with an allergy to Benadryl may experience an upset stomach. This can manifest as loss of appetite, discomfort, or changes in behavior due to nausea.

Skin Rashes

Skin rashes are another sign that a dog might be allergic to Benadryl. These can present as redness, itchiness, or visible hives on the skin.

Elevated Heart Rate

An elevated heart rate can occur in some dogs who are allergic to Benadryl. This can be dangerous, especially in dogs with pre-existing heart conditions, and requires immediate veterinary attention.

Can Benadryl Interact Negatively with Other Medications My Dog Is Taking?

Yes, Benadryl can interact negatively with certain medications your dog might be taking, including tranquilizing medications, amlodipine, gabapentin, lisinopril, prednisone, and valium.

Benadryl, also known as diphenhydramine, is an antihistamine often used to alleviate allergy symptoms in dogs.

However, it can have negative interactions with other medications. For instance, if your dog is on tranquilizing medications, the tranquilization effect can be excessively intensified when combined with Benadryl, potentially leading to severe drowsiness or sedation.

Other medications that can have negative interactions with Benadryl include amlodipine, gabapentin, and lisinopril.

When these drugs are taken with Benadryl, they could cause excessive drowsiness and impaired cognitive function.

Additionally, Benadryl should not be used in dogs that are on prednisone and valium due to potential negative interactions.

There have been reports of fatal poisoning in dogs due to the co-ingestion of diphenhydramine and ethanol.

Is Benadryl Harmful to Senior Dogs or Dogs with Weakened Immune Systems?

Yes, Benadryl can potentially have negative effects on senior dogs or dogs with weakened immune systems, particularly if not administered in the correct dosage or if these dogs have certain pre-existing conditions.

Senior dogs often have less efficient metabolism and elimination systems, which means that drugs like Benadryl can stay in their system for longer, increasing the risk of potential side effects. These can include drowsiness, dry mouth, urinary retention, and occasionally, hyperexcitability.

Furthermore, dogs with weakened immune systems may be more susceptible to the side effects of Benadryl. These dogs might already be on other medications, increasing the risk of drug interactions.

What Should I Do If I Suspect My Dog Has Had an Adverse Reaction to Benadryl?

If you suspect that your dog has had an adverse reaction to Benadryl, you should immediately contact your veterinarian or an emergency veterinary hospital.

Recognize the Signs

The first step is to recognize the signs of an adverse reaction to Benadryl, which can include symptoms like lethargy, dry mouth, urinary retention, vomiting, diarrhea, lack of appetite, and unusual excitement.

More severe signs of a Benadryl overdose could include seizures, rapid heartbeat, agitation or hyperexcitability, dilated pupils, constipation, slow or shallow breathing, red rashes on the skin, swelling of the face and tongue, and skin chewing.

Seek Immediate Veterinary Care

Once you’ve identified these symptoms, it’s crucial to seek immediate veterinary care. Contact your veterinarian or an emergency veterinary hospital right away. In cases of suspected overdose, you could also call a Pet Poison Helpline.

Follow Up Evaluation

Even if your pet’s symptoms seem mild and they appear to respond to treatment, it’s still important to follow up with your veterinarian. They can conduct further evaluations to ensure there are no lasting effects from the adverse reaction, and provide guidance on whether it’s safe to continue using Benadryl in the future.

Avoid Self-Medication

To prevent such situations in the future, avoid self-medicating your pet. Always consult with a veterinarian before administering any over-the-counter medication like Benadryl to ensure it’s safe for your pet and that you’re using the correct dosage.


Q: What is Benadryl?

A: Benadryl is the brand name for the drug called Diphenhydramine, which is an antihistamine commonly used to relieve symptoms of allergies in humans.

Q: Can Benadryl be used to treat dogs with allergies?

A: Yes, Benadryl can be used to treat certain allergies in dogs, such as itchy skin, insect bites, or allergic reactions to vaccines.

Q: How does Benadryl work?

A: Benadryl works by blocking the effects of histamine, which is a substance released during allergic reactions. By blocking histamine, it helps relieve symptoms like itching, swelling, and runny nose.

Q: Can I give my dog Benadryl for motion sickness?

A: Benadryl may help with mild cases of motion sickness in dogs, but it is best to consult your vet for proper dosage and alternative options.

Q: How much Benadryl can I give my dog?

A: The recommended dosage of Benadryl for dogs is 1mg per pound of body weight. However, it is crucial to consult your veterinarian for the correct dosage based on your dog’s specific needs.

Q: Are there any side effects of giving Benadryl to dogs?

A: Some possible side effects of Benadryl in dogs may include drowsiness, dry mouth, urinary retention, or gastrointestinal upset. It is important to monitor your dog for any adverse reactions and consult your vet if you have any concerns.

Q: Can I give my dog any form of Benadryl?

A: It is recommended to give your dog Benadryl in tablet or liquid form, specifically formulated for dogs. Avoid using any Benadryl product that contains additional active ingredients, such as decongestants, as they can be harmful to your dog.

Q: Can I use Benadryl to sedate my dog?

A: Benadryl should not be used as a sedative for dogs. If you are considering sedating your dog for travel or other reasons, it is best to consult your vet for appropriate medications.

Q: What should I do if my dog has an allergic reaction and I don’t have Benadryl?

A: If your dog has a severe allergic reaction and you don’t have Benadryl available, it is essential to seek immediate veterinary assistance. Severe allergic reactions can be life-threatening and require prompt medical attention.

Conclusion and final thoughts

In conclusion, Benadryl can be used to treat some allergies in dogs and relieve symptoms of itching, but it’s important to use the correct dosage.

Speak with your veterinarian before giving Benadryl to your dog, as an overdose can lead to serious health problems.

Additionally, discuss all possible alternative treatments before opting for this over-the-counter drug. When used correctly, Benadryl can be a safe and effective way to treat canine allergies and itching.

Please take the time and leave a comment below if this article helped you, or you have any additional questions.

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