Benadryl, known scientifically as diphenhydramine, is a medication widely recognized for its use in humans, particularly for treating various allergy symptoms such as sneezing, runny nose, watery eyes, hives, skin rash, and itching.

It’s also used for other purposes, such as treating motion sickness, inducing sleep, and alleviating certain symptoms of Parkinson’s disease​​. However, Benadryl’s usage extends beyond human health; it is also commonly employed in veterinary medicine, particularly for dogs.

Benadryl (Diphenhydramine) Injection For Dogs

When it comes to dogs, veterinarians frequently use diphenhydramine (the active ingredient in Benadryl) to treat a range of conditions.

Benadryl for Dogs Side Effects & Adverse Reactions

Understanding the potential side effects of Benadryl shots in dogs is vital for pet health and safety. Given that pets, like humans, can experience varying reactions to medications, it’s important for pet owners to be informed about what to expect and when to seek veterinary assistance.

This article aims to discuss these aspects in detail, providing pet owners with essential information for making informed decisions about their pets’ health care.

What is Benadryl Shot and How is it Used in Dogs?

Benadryl, or diphenhydramine, is classified as a first-generation antihistamine. It works by competitively inhibiting H1 receptors, thereby blocking the action of histamine, a substance in the body responsible for allergic symptoms.


This mechanism makes it effective in treating various allergic conditions in both humans and animals​​.

In dogs, Benadryl is used for a variety of reasons:

  • Allergies: Similar to its use in humans, it’s effective in treating allergic reactions in dogs, such as those caused by environmental factors or insect bites.
  • Motion Sickness: For dogs that experience discomfort during travel, Benadryl can help alleviate motion sickness.
  • Sedation: It has sedative properties that can be useful in managing anxiety, particularly travel anxiety.
  • Anaphylaxis and Allergic Reactions: In cases of severe allergic reactions, Benadryl can be a crucial part of the treatment plan.
  • Atopy and Mast Cell Tumors: It’s also used in the management of atopy (chronic itchy skin condition) and, in some cases, to treat mast cell tumors, a type of cancer that can affect dogs.

It’s important to note that while Benadryl is generally safe for dogs, its administration should always be under the guidance of a veterinarian.

This is to ensure that the correct dosage is given and to monitor for any adverse reactions or interactions with other medications the dog might be taking​​​​.

Administering Benadryl to Dogs: Shots vs. Oral Medication

Benadryl (diphenhydramine) can be administered to dogs either orally or via injection. Oral administration can be in the form of a tablet, capsule, or liquid, and it can be given with or without food. However, it’s important to note that if a dog vomits after dosing on an empty stomach, future doses should be given with food or a treat.

The injection, on the other hand, is typically administered in a veterinary hospital setting and can be given intravenously, intramuscularly, or subcutaneously. This medication generally takes effect quickly, within about 1 to 2 hours, and improvement in clinical signs should follow​​.

The choice between an injection and oral medication may depend on several factors, including;

  • the severity of the condition being treated
  • the dog’s ability to tolerate oral medication
  • and the urgency of the treatment

In cases where rapid onset of action is needed, or if a dog is unable or unwilling to take oral medication, an injection may be preferred.

Common Side Effects of Benadryl in Dogs


Benadryl can cause several side effects in dogs. The most common ones include:

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

Less common side effects may include vomiting, diarrhea, rapid heartbeat, decreased appetite, and difficulty breathing.

These typically occur within the first hour of administration, so it’s important to closely monitor your dog during this period. If any concerning symptoms are observed, contact a veterinarian immediately​​.

Serious Side Effects and Risks


In cases of overdose or hypersensitivity, Benadryl can lead to more severe side effects, including:

  • Agitation
  • Constipation
  • Depression or hyperactivity
  • Dilated pupils

If any of these symptoms are observed, it’s crucial to seek veterinary attention immediately.

Additionally, Benadryl should be used cautiously or avoided in dogs with certain health conditions, such as;

  • cardiovascular disease
  • lung disease
  • bladder issues
  • enlarged prostate
  • high blood pressure
  • glaucoma
  • epilepsy or seizures
  • and in cases of previous adverse reactions to the drug

It’s also advised to consult a veterinarian before giving Benadryl to young puppies, pregnant or nursing pets, and when combining it with other medications​​.

Please note that while this information provides a general overview, it’s always best to consult with a veterinarian for advice tailored to your specific dog’s health needs.

Dosage and Safety Precautions for Benadryl in Dogs

When administering Benadryl to dogs, it’s crucial to follow proper dosage guidelines and take safety precautions. According to the Merck Veterinary Manual, the standard dose for Benadryl in dogs is typically between 2 to 4 milligrams per kilogram of body weight, administered two to three times daily.

It’s important to monitor your dog closely after administering Benadryl for signs of adverse reactions, as diphenhydramine may interact with other medications.

Consult with your veterinarian to determine if Benadryl is safe to use in conjunction with other drugs your dog may be taking, including;

  • epinephrine
  • tranquilizers
  • antifungals
  • heparin
  • barbiturates
  • and some antibiotics​

Alternatives to Benadryl for Dogs

If the side effects of Benadryl, such as dry mouth, sleepiness, and urine retention, are a concern, or if your dog has certain health conditions, there are natural alternatives available.

For allergies, popular natural antihistamines include;

  • Stinging Nettle
  • Quercetin
  • and certain foods like fresh meats, fish, eggs, and non-citrus fruits
  • CBD oil has also shown potential benefits for seasonal allergies and itching

For motion sickness, herbs like Ginger, Peppermint, Catnip, Fennel, and Dill, which have anti-nausea properties, may be helpful. CBD oil has been identified as an effective anti-vomiting compound.

Anxiety in dogs can be addressed with natural solutions like exercise, essential oils, grooming, music, pheromones, massage, and supplements, including CBD oil​.


Can all dogs take Benadryl shots?

While Benadryl is safe for many dogs, it’s not suitable for all. Dogs with certain health conditions should avoid Benadryl. Always consult a veterinarian before administering Benadryl to ensure it’s safe for your specific dog​​.

How quickly does a Benadryl shot take effect in dogs?

The effects of Benadryl generally last between 8 to 12 hours, and the drug is usually given two to three times daily​​.

Can Benadryl shots interact with other medications my dog is taking?

Yes, Benadryl can interact with other medications. It’s important to consult with a veterinarian to ensure there are no potential drug interactions​​.

How can I tell if my dog is having an adverse reaction to a Benadryl shot?

Watch for signs such as difficulty urinating, dry mouth, excessive drooling, lethargy, rapid breathing, unsteady walking, agitation, or dilated pupils. If any of these symptoms are observed, contact your veterinarian immediately​​.


In summary, Benadryl (diphenhydramine) can be a safe and effective medication for dogs when used correctly. The standard dosage is typically 1 to 2 mg per pound of body weight, administered two to three times daily.

It’s vital to monitor your dog for any side effects and consult a veterinarian before administering Benadryl, especially if your dog is on other medications.

Natural alternatives to Benadryl include certain herbs, foods, and CBD oil, which can be used to treat allergies, motion sickness, and anxiety.

Always consult a veterinarian for personalized advice and treatment plans for your dog, ensuring the safest and most effective care.

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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