Benadryl® Dosing for Dogs: How to Use It Safely

If your dog has allergies or an allergic reaction, you may be looking to see if Benadryl is safe and what dose to use. Benadryl® (Diphenhydramine) is an antihistamine that we use to relieve allergy symptoms such as itching, hives and swelling. In this post, I will outline everything you need to know about using Benadryl for dogs.

What is Benadryl and How Does It Work?

Benadryl, also known as diphenhydramine HCl, is a first-generation antihistamine. This medication reduces histamines that cause itching, swelling, sneezing, and other allergic symptoms. Benadryl can cross the blood-brain barrier, which can be helpful in reducing nausea and vomiting.

While Benadryl is a common over-the-counter option, our team at Kingsdale Animal Hospital always recommends a quick consultation with your vet before starting any new medication to ensure there are no underlying contraindications.

A Quick Tip: How Much Benadryl Can You Give Your Dog?

The maximum dose of Benadryl that I recommend is 4 milligrams per kilogram of body weight (i.e. 4mg/kg).

Some guidelines:

• A small dog weighing around 10 pounds (4.5 kg) should receive no more than 18 mg.
• A medium-sized dog weighing 25 pounds (11.3 kg) could be given up to 45 mg.
• For larger dogs around 50 pounds (22.7 kg), the maximum amount is 90 mg.

Remember, these are just examples. For the most accurate dosage specific to your dog, see the chart below. Also, make sure you talk with your veterinarian before giving Benadryl to your dog.

Determining the Right Benadryl Dosage for Dogs

We dose Benadryl on a weight basis, specifically milligrams per kilogram of body weight (mg/kg). My recommended dose range is 2 to 4 mg per kg (or 1 to 2 mg per pound) of your dog's weight.

Benadryl Dosage Chart for Dogs

The following Benadryl dosage chart for dogs serves as a reference, and it is important to note that it should not replace professional guidance or recommendations from your veterinarian. Doses can be repeated every 8 hours as needed.

If your dog has mild symptoms, you can likely start at the lower end of the dosing range. If your dog is experiencing an allergic reaction, using the higher dose will be more beneficial.

I have also learned that when using Benadryl for dogs with allergies, starting it early in the course of symptoms seems to work better for dogs.

Also, keep in mind that the sedating effects of Benadryl can and will vary between dogs. Some dogs will show no sedation, others will be very sedated. Typically, it is dose-dependent, where the higher the dose, the more sedation you can expect.

The Main Uses of Benadryl for Dogs

Benadryl is a versatile medication and can address a variety of conditions:

• Allergic reactions
• Vaccine reactions
• Preventative relief if you foresee the need for it. Examples would be trail walks or through known areas that might induce an allergic response.
• Anxiety and motion sickness (although Cerenia would likely work better for this).
• Mast-cell tumour treatment. We typically would give Benadryl prior to surgical removal of a known mast cell tumour, as well as for a few days beyond surgical removal.

Potential Side Effects and Important Information

Benadryl is generally well-tolerated by many dogs, and here are the side effects you may notice:

• Drowsiness, although not as pronounced as it is in people
• Sedation
• Digestive upsets like diarrhea or vomiting. It can be reduced if given with food.
• Agitation, more common at higher doses
• Seizures
• Dry mouth
• Constricted pupils
• Urinary retention

If your dog has conditions such as glaucoma, heart disease or seizures, please discuss in detail with your veterinarian to determine if Benadryl is the right choice for your dog.

🚨 NEVER give your dog an "Allergy and Sinus" form of Benadryl or any antihistamine to your dog. The sinus component often refers to the addition of pseudoephedrine, which is extremely toxic to dogs. Make sure your Benadryl ONLY contains diphenhydramine as the medicinal ingredient.

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