Diphenhydramine Hydrochloride for Dogs

Diphenhydramine hydrochloride, also known as Benadryl, is an antihistamine that’s commonly used to treat canine allergies. Although it’s not officially licensed for veterinary use, it’s the most commonly used canine antihistamine.

Let’s look at how diphenhydramine helps an allergic dog combat his symptoms, what its common side effects may be and if there are situations in which its use is not recommended.

How Diphenhydramine Can Help an Allergic Dog

As an antihistamine, diphenhydramine helps control production of histamine, a chemical your dog’s immune system creates in response to a perceived threat to his health that’s known as an allergen. Common allergens include food ingredients, flea saliva, dust mites or pollen. Histamine is what causes your dog’s allergic reactions, such as hives, irritated or itchy skin and swelling.

Diphenhydramine helps control atopic allergies in your dog, which are those allergies that show symptoms on his skin but are caused by an inhaled substance. It is also effective at controlling allergic reactions to vaccinations, food ingredients, insect stings and snake bites.

In addition to its use as an antihistamine, diphenhydramine helps control motion sickness, muscle tremors and vomiting. It can also be an effective sedative.

Diphenhydramine is available in tablet, liquid or injectable forms. Your dog’s weight will determine his daily medication dose. Discuss dosage instructions with your veterinarian carefully, and do not attempt to use this medication on your dog without consulting your veterinarian.

Be sure to give your pet medication that contains only diphenhydramine. Some versions of the medication include pain relievers or human sinus medications that could be harmful to your dog’s health.

Common Side Effects of Diphenhydramine

The most common side effect of diphenhydramine is sleepiness. Other common side effects of the medication include:

  • appetite loss
  • diarrhea
  • dry mouth
  • lethargy
  • vomiting

Some dogs may be allergic to diphenhydramine. Symptoms of an allergic reaction to the medication include:

  • cold limbs
  • facial swelling
  • hives
  • pale gums
  • seizures

If you suspect your dog is allergic to diphenhydramine, stop giving him the medication and contact your veterinarian’s office for further treatment instructions.

In other cases, your dog may accidentally take an overdose of diphenhydramine. Symptoms of overdose include:

  • Coma
  • Extreme excitability
  • Extremely dry eyes and mouth
  • Low blood pressure
  • Rapid heartbeat

Contact your veterinarian’s office or an animal emergency clinic immediately if you suspect your dog has overdosed on diphenhydramine because he will require urgent care to restore his health.

When Diphenhydramine Should Not Be Used on an Allergic Dog

Although diphenhydramine is generally considered safe, it is not recommended for all dogs. Do not give diphehydramine to dogs with the following medical conditions:

  • asthma
  • bladder obstruction
  • enlarged prostate
  • glaucoma
  • heart disease
  • hypertension
  • hyperthyroidism
  • obstructive pulmonary disease

The common side effects of diphenhydramine may make these medical conditions worse, which is why its use is not recommended for these dogs.

The safety of giving diphenhydramine to pregnant or nursing females is unknown. The medication is not recommended for therapy or working dogs because of its sedative side effects.

Diphenhydramine will affect the outcome of skin allergy tests. If your dog requires skin allergy tests, you will need to work with your veterinarian as to when you should stop administering diphenhydramine before the test and when you can resume the medication after the test.