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Benadryl For Dogs

Benadryl for Dogs: Indications, Considerations, and Everything Else You Should Know

Benadryl is among the many human over-the-counter medications that can also be administered to dogs. Chances are your vet advised you to give Benadryl for dogs if your fur baby is suffering from allergies or motion sickness.

However, you don’t just go out, buy Benadryl tablets, and give it to your dog right away. There are many considerations in using Benadryl for dogs.

This post aims to inform you about everything you need to know about Benadryl for dogs. We’ll discuss what Benadryl is, why it is given to dogs, dosages, methods of administration, and other special considerations regarding this medication for dogs.

What is Benadryl?

Benadryl is the brand name of the medication diphenhydramine.

Benadryl Info graphic 

Benadryl is classified as an antihistamine. This medication is used in humans to treat a variety of cold and allergy symptoms such as:

Benadryl Treats Info graphic

People suffering from motion sickness and insomnia also take Benadryl to ease their symptoms.

There are various strengths and formulations of Benadryl in the market. The most common dosage available is 25 mg in pink-colored tablets. There is also a liquid-gel formulation in 25 mg strength for those who find it hard to swallow tablets.

Stronger dosages are available in 50 mg, marketed as Benadryl Extra Strength and Benadryl Nighttime. A liquid formulation branded as Benadryl Elixir/Benadryl Syrup is also available at a dosage of 12.5mg/5ml.

Children’s formulas are also available in liquid form. The medication does not contain alcohol and is generally milder than the adult formulation.

Benadryl Formulation in dogs bark for more

Conditions Where Benadryl is Used for Dogs

Benadryl is indicated for dogs to relieve the following conditions:

1. Allergies

Benadryl is effective at relieving symptoms of dog allergies. Here are some types of allergies in dogs that Benadryl may help alleviate:

Types Of Allergies in Dogs Info graphic

Anaphylactic reactions are severe and life-threatening reactions that a dog may experience during an allergy. The onset is sudden and may be caused by an insect bite or administration of medication he’s allergic to. Anaphylactic reactions are very rare, but it’s best to know what your dog’s allergies are to avoid getting an anaphylactic reaction in the future.

Note that signs and symptoms of allergies in dogs may be a bit different to those experienced by humans. For instance, red, itchy, and inflamed eyes may signal allergies in humans right away, but a dog experiencing this may have other infections such as respiratory illnesses. 

Hence, you must make sure that your dog is indeed suffering from an allergy before giving Benadryl for dogs. Take your dog to the veterinarian first and let the veterinarian assess your pooch so that you’re sure of his condition before giving Benadryl.

2. Hives

Hives in dogs is an allergic reaction typically characterized by intense itching and swelling in the skin. The swelling looks like several raised wheals appearing on the skin. Hives may develop anywhere in the body, but it is mostly seen on the neck, back, eyelids, flanks, and legs. 

Severe cases of hives in dogs may include symptoms such as:

Hives on Dogs Bark for More infographic

Hives occur 6-24 hours on average after being exposed to the allergen. However, it can also occur a few minutes after being exposed to the causative agent.

Other than allergens, hives can also be caused by certain medications and dog shampoos. Contact with chemicals and certain toxic plants may also trigger a hives flare-up.

You can quickly see hives in short-coated pooches, but it’s a bit more challenging for dogs with long hair. You need to feel them on your dog’s skin underneath the long hair.

Mild hives cases don’t require any treatment, as the itching and swelling disappear rapidly after a few hours. However, persistent hives often need to be treated with rapid-acting corticosteroids. Another option is giving Benadryl for dogs with hives.

3. Motion Sickness

Motion sickness in dogs happens when the ear fluids that allow your dog to orient itself to the outside world moves too much. This may be a result of excessive motion such as when your pooch is in a car ride for the first time. 

Ear fluids related to motion and orientation normally move around, but too much movement may cause true nausea and motion sickness. Other symptoms may also appear, such as:

Motion Sickness in dogs barkformore infographic

Studies have shown that surgery requiring the inactivation of a dog’s semicircular canals may lead to lesser chances of getting motion sickness. However, not everyone wants their animals to undergo surgery, and for that, Benadryl is an effective alternative. Many veterinarians recommend Benadryl to help ease car sickness.

4. Anxiety

Dogs can also suffer from anxiety and stress, just like people do. There are different kinds of anxiety in dogs, such as:

Anxiety in dogs barkformore infographic

  • Separation anxiety – The most common form of dog anxiety. Here, the dog feels tremendous anxiety when he is separated from his humans.
  • Fear of loud noises – Fireworks or thunderstorms may trigger anxiety in dogs. This is because dogs’ hearing is far more superior than humans (1). Dogs can hear high-pitched sounds of up to 45,000 Hertz and can hear four times better than humans. Hence, loud noises for humans sound even louder for dogs, triggering their anxiety.
  • Changes in routines and environment – These may include riding a car, going to a vet clinic, traveling with owners via planes, or even a change in the owner’s working hours.

Keep an eye out for these signs of anxiety in dogs:

  • Pacing and panting frequently, even when the weather is cool
  • Digging
  • Escaping
  • Shivering
  • Howling and barking when the owner isn’t around
  • Cowering in one corner
  • Not eating
  • Excessive licking and chewing
  • Frequent urination
  • Inability to settle down

Sometimes, anxiety symptoms can be so subtle it’s hard to recognize. These signs may include looking away, paw lifting, lip licking, and showing his eye’s whites.

Medications may be required if the dog’s anxiety levels are so high it depresses their functions and behaviors. Benadryl is one safe medication you may give to calm down your dog. Note that this should be under the advice of your dog’s veterinarian.

Untreated anxiety may cause eventual harm to your dog. This anxiety might scale up to aggressive behaviors such as self-harm, destroying things, or running away. Hence, you can give your dog Benadryl to ease his anxiety. Gentle but firm behavioral training is also recommended to minimize behavioral problems that may arise with anxiety (2).

5. Heartworm Disease

Heartworm is a serious illness transmitted by mosquito bites. It is caused by Dirofilaria immitis, a parasitic worm that lives inside a dog and infects the heart, lungs, and blood vessels of adult dogs (hence the term heartworm). Heartworms can live on a dog’s body for 5-7 years.

Heartworm Disease infographic

There are certain medications given to dogs with heartworm disease. These medications either kill adult heartworms inside a dog’s body or kill the microfilariae (offspring of the heartworms) contained in the dog’s bloodstream. 

These medications are aggressive and may cause allergic reactions to dogs. Hence, Benadryl is often used to manage symptoms associated with heartworm disease treatment.

6. Mast Cell Tumors

Mast Cell Tumors are common in dogs. These tumors are characterized by small and freely movable tumors found in the skin and subcutaneous tissues. 

Some tumors are more aggressive, though. These larger tumors are often hairless and ulcerated with inflammation in the surrounding areas. Such tumors may present with other symptoms such as:

Mast Cell Tumor infographic bark for more

Mast cell tumors tend to trigger a release of histamine. This happens during mast cell degranulation, or when the mast cells release various chemicals and compounds including histamine. 

When histamine is released in massive proportions, allergic symptoms such as itchiness will appear. Hence, veterinarians may advise you to give Benadryl for dogs to ease the symptoms of histamine release.

Benadryl’s Mechanism of Action in Dogs

Histamine is a chemical released by the dog’s immune system in response to the foreign presence in the dog’s body. Now, various parts of the body have histamine receptors that activate whenever histamine is released into the bloodstream. Receptors are commonly found in the skin, gastrointestinal tract, and urinary tract.

Histamine is responsible for the uncomfortable symptoms associated with allergic reactions. Remember that during an allergic reaction, a foreign substance invades the dog’s body, causing the immune system to release histamine.

Diphenhydramine (Benadryl’s generic name) works by blocking histamine reception in the body. The drug then alleviates the unpleasant allergic symptoms created by histamine. The dog’s body continues producing histamine, but Benadryl blocks it from being absorbed by the receptors.

Diphenhydramine is classified as a first-generation ethanolamine-derivative antihistamine. This simply means that the drug crosses the blood-brain barrier as opposed to other antihistamines. And as such, Benadryl is highly-effective in combating allergic symptoms in dogs. However, this also means that the risk of adverse effects in dogs may also be greater than second-generation antihistamines.

Correct Dosage of Benadryl for Dogs

There is no specific pre-set dosage of Benadryl for dogs yet. The best thing to do is to consult your veterinarian for advice regarding the correct dosage of Benadryl for your dog’s specific condition.

Meanwhile, the Merck Veterinary Manual generally recommends Benadryl dosage of 2-4mg per kilogram of your dog’s body weight. This translates to 1mg of Benadryl for every pound of body weight. The medication may be administered 2-3 times daily, eight hours apart. Effects can be seen as early as 30 minutes after drug administration.

Benadryl often comes in 25mg tablets. Hence, a 25-pound dog can safely take one tablet in a day.

Here are some considerations regarding the type of Benadryl to use for your dog:

  • Make sure that the Benadryl variant you’re using only contains diphenhydramine HCl. Several variants contain components other than diphenhydramine HCl, which can be harmful to dogs.
  • Use only the tablet form for dogs. Steer clear of liquid Benadryl as these drugs contain alcohol, a substance harmful for dogs. Avoid giving time-release capsules as well.
  • Small dogs may be given liquid formulations of Benadryl. Kid’s liquid Benadryl doesn’t contain alcohol. Plus, it’s also easier to dose and gives to small dogs via a syringe.
  • If your main concern is skin itchiness, you can use a special topical formula of Benadryl. Ask for your vet’s advice regarding the use of Benadryl gels or creams.
  • If you happen to miss a Benadryl dose, give it as soon as you remember. However, skip it when the proper time for the next dose is too near already.

Proper Dose of Benadryl in dogs inforgraphic bark for more

Again, consult your dog’s veterinarian first before deciding on a dosage to give to your dogs. This is the safest way to determine the correct dosage of Benadryl for dogs, depending on the condition your dog is experiencing.

Benadryl Side Effects in Dogs

Side effects of Benadryl for dogs include the following:

  • Excessive salivation
  • Dry mouth
  • Fast heart rate
  • Rapid breathing
  • Sedation
  • Urinary retention

Rarer side effects may also occur. Hence, keep an eye out for the following:

  • Appetite changes (sudden decrease or increase)
  • Vomiting
  • Diarrhea

Side effects in benadryl in dogs barkformore

Carefully monitor your dog for side effects one hour after the administration of Benadryl. Most incidences of side effects happen after an hour of ingesting Benadryl.

Overdose of Benadryl in Dogs

Benadryl overdose is possible in dogs. These are the symptoms you need to watch out for:

Benadryl Overdose in barkformore infographic

  • Very rapid heartbeat
  • Agitation
  • Dilated pupils
  • Constipation
  • Seizures

All these symptoms signal that the central nervous system has been affected and is displaying hyper-excitability. These symptoms may eventually be fatal for your dog. Hence, immediately take your dog to the veterinarian if you spot any of these symptoms right away.

Benadryl Allergy in Dogs

At times, a dog may be allergic to Benadryl itself. Hence, always keep a close eye on your dog if you gave him Benadryl for the first time.

Benadryl is often used to treat allergic symptoms. Hence, you can sense a Benadryl allergy if your dog’s symptoms worsened after Benadryl administration. If itching, hives, and swelling intensify, seek the help of your veterinarian immediately. Remember that severe allergic reactions could lead to fatal anaphylactic reactions when not treated promptly.

Avoiding Benadryl in Certain Conditions

Benadryl for dogs must not be given during the following conditions:

Avoiding Benadryl in dogs infographic barkformore

  • Pregnancy
  • Angle-closure glaucoma
  • Seizure disorders
  • Hypertension
  • Low blood pressure
  • Severe heart failure
  • Allergic lung disease
  • Bladder neck obstruction
  • Prostatic hypertrophy
  • Hyperthyroidism

Most vets do not recommend Benadryl for pediatric or neonatal dogs. Lactating mother dogs should also avoid Benadryl.

Consult your dog’s veterinarian for alternative treatment and/or medications your dog can receive instead of Benadryl.

Drug Interactions with Benadryl

Make sure that your veterinarian is aware of your dog’s Benadryl use. This is because certain drugs may interact with Benadryl and cause more problems in your dog. Drugs that may interact with Benadryl include:

  • Anticholinergic drugs like atropine
  • Drugs that depress the central nervous system like anti-anxiety medications and sedatives
  • Tricyclic antidepressants such as amitriptyline

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Is Benadryl Safe for Dogs?

Yes, Benadryl for dogs is generally safe. It doesn’t have an FDA-approval for dog use yet, though. But many veterinarians recommend Benadryl and even use it in their clinical practice, as the medication is seen as highly effective. Another thing is that Benadryl has a wide safety margin in both humans and dogs.

If you’re wary of using Benadryl for dogs, speak to your dog’s veterinarian first to clear out any further questions you have in mind.

The Bottomline

Benadryl can safely be used to treat a variety of allergic symptoms and conditions in dogs. It is also used to calm a dog’s anxiety, and as a conjunction in heartworm and mast cell tumor treatments. Most veterinarians recommend using tablet forms in dosages of 2-4mg/kg body weight. Smaller dogs may benefit from children’s formulas of Benadryl.

Always ask your doctor’s advice regarding Benadryl for dogs. There are several considerations regarding the safe dosage, drug interactions, and contraindications for Benadryl use. Nevertheless, Benadryl is an effective and safe medication you can give to your dogs upon approval from your vet.


(1) Dunbar, C. (2018). Dogs: 101 amazing dog fun facts and trivia for kids.

(2) Applebaum, S. (2004). ABC practical guide to dog training. Wiley Publishing, Inc.merc

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