Other health problems

Benadryl for Dogs: Guide for Dosage, Side Effects and Safety

Josie F. Turner
By Josie F. Turner, Journalist specialized in Animal Welfare. Updated: August 26, 2020
Benadryl for Dogs: Guide for Dosage, Side Effects and Safety

See files for Dogs

You may have heard of the use of Benadryl for humans, as it is a popular antihistamine medicine. While we may think of dogs as being the ones which cause allergies, dogs can suffer just like their human guardians. If we go to the veterinarian, there are different types of allergy medication for dogs. Which type of medication will depend on the type of allergy. In this AnimalWised article, we look at Benadryl for dogs: a guide for dosage, side effects and safety.


  1. Can I give my dog Benadryl?
  2. What is Benadryl for dogs used for?
  3. Can you give my dog Benadryl to calm him down?
  4. When is Benadryl for dogs not safe?
  5. How much benadryl should I give a dog?
  6. How long does benadryl take to work in dogs?
  7. Side effects of benadryl in dogs
  8. Alternatives to benadryl for dogs

Can I give my dog Benadryl?

Benadryl is an over-the-counter allergy medication which is classified as an antihistamine. We should know that we giving a dog human medication is not a given that it is safe. Active ingredients in various drugs have an effect on dogs different to humans, not to mention the size difference means the dosage is an important factor.

Fortunately, Benadryl is generally safe for canine consumption. However, as with any medication, its safety depends on the dosage, how it is administered and other factors concerning the health of the dog. Even if we can purchase Benadryl over the counter, we need to ask our veterinarian first if we want to treat our dog's allergies.

However, there is a significant factor we need to consider. Benadryl in the USA and Canada uses diphenhydramine, but the UK version of this product uses cetirizine or acrivastine. While diphenhydramine has solid research behind it in veterinary medicine, neither of the UK antihistamine types are very well studied in dogs. For this reason, we cannot confirm its safety and should generally be avoided.

What is Benadryl for dogs used for?

Benadryl is the commercial name of diphenhydramine in the US. Thisis a tyoe of antihistamine that works by blocking H-1 receptors, the histamine receptors in charge of producing the inflammation caused by allergies.

A vet will prescribe benadryl for your dog in different situations, the most common being the following:

  • Relieving symptoms of allergy in dogs: this drug can help reduce the most common symptoms of allergies, including itching, hives, swelling, redness, runny nose and eyes, coughing, sneezing, anaphylactic reactions. This is the most common use of Benadryl for dogs. In this sense, it can also be used after a bad reaction to an insect's sting or bite. However, if a dog goes into anaphylactic shock, they will need veterinary medical attention immediately.
  • Mitigating mast cell tumors: dogs with mast cell tumors release a lot of histamine caused due to mast cell degranulation. Benadryl or other diphenhydramine products can help mitigate the effects of its release. However, treatment will need to be prescribed by a veterinarian.
  • As part of heartworm treatment: this drug can be prescribed by vets occasionally to prevent the allergic reactions that sometimes accompany this condition.
  • Insomnia: although melatonin is usually used for sleeping issues in dogs, Benadryl may also be prescribed for this purpose by a vet in some cases.
  • Travel sickness: dogs that suffer from motion sickness by getting dizzy when travelling can also be prescribed diphenhydramine by a vet, as it is very similar in content to dimenhydrinate.
  • Anxiety: this is not the most prescribed treatment, but in some cases of situations in which a dog suffers from anxiety, a vet may also suggest the use of this drug due to its sedative properties to calm the dog's nerves.

Note that, although it is commonly prescribed by vets, this drug has not yet been approved for veterinary use by the FDA[1].

Benadryl for Dogs: Guide for Dosage, Side Effects and Safety - What is Benadryl for dogs used for?

Can you give my dog Benadryl to calm him down?

As we'll explain in further detail later on, one of Benadryl's side effects is drowsiness, which is why it can calm a dog down and make them sleepy. Many people know about this effect, which is why they think it can be a good remedy to calm a nervous dog down. However, it is not recommended to medicate your dog without your vet's previous consent.

Some people think that Benadryl is good to calm hyperactive dogs. Hyper dogs can be a handful and it may be tempting to give the dog medication to sedate them. However, this is treating the symptom and not the problem. To calm a hyperactive dog, you will need to engage them, provide plenty of exercise, remove unnecessary stressors and go to a canine ethologist in acute case.

Also, if you try to medicate a hyper dog with Benadryl regularly, you will end up causing serious harm due to prolonged use. It will also make the drug ineffective if they need it for allergies and it will increase the likelihood of negative side effects.

Stress and anxiety can also cause a dog to be hyperactive, leading us to wonder if we can give them Benadryl to calm them. Cases of anxiety in dogs should be treated by your vet, and only in severe cases is any type of medication prescribed.

When is Benadryl for dogs not safe?

It is also important to know in which cases it is not safe to give your dog Benadryl. Although it is an allergy medication, it is possible a dog will be allergic to some of the ingredients in it. Other than being allergic, Benadryl for dogs is contraindicated for several conditions:

  • Glaucoma: although you may think that eye redness in dogs is a symptom of allergy, this can also indicate glaucoma, a condition that can worsen if you give your dog Benadryl.
  • Pregnancy: female dogs that are expecting or are currently breastfeeding should not be given this medicine under any circumstances as it can affect the health of the newborn puppies.
  • When using other drugs: if your dog has been prescribed any other form of anticholinergic drug (drugs that block a certain neurotransmitter) you should not combine it with diphenhydramine as it can cause toxicity.
  • Depression: the calming effect of this drug can worsen your dog's depression, especially if they are being medicated for this condition too.
  • Prostate enlargement: if your dog has prostate cancer or another reason for having an enlarged prostate, we should not give them Benadryl.
  • Hyperthyroidism: the same goes for dogs with an overactive thyroid.

How much benadryl should I give a dog?

You should only give a dog Benadryl, and not any of its other products such as "Benadryl sinus" or "Benadryl itch cooling gel" because it can contain ingredients such as xylitol, camphor, Tylenol or alcohol that are bad for your dog. There are different forms of Benadryl and, although you can use them in pills and liquid form, you should never give them Benadryl time-release capsules (pictured above) due to the dog's body's absorption. Once the vet has indicated the exact medication and you have listened carefully to their instructions, you can proceed to give your dog this medicine, but in the right amount.

The vet should indicate the right amount of Benadryl to give your dog depending on their condition, although recommendations say that you should give your dog from 2 to 4 mg per kilo (1 to 2 mg per pound) your dog weighs. For example, how much Benadryl for a 10 pound dog? The answer is between 10 to 20 mg per dose. It should be given to your dog two to three times daily or every 8 to 12 hours.

In liquid form, it is recommended to give a dog no more than 0.4ml per pound your dog weighs. If your dog weighs 10 pounds, you should give them 4 ml liquid Benadryl.

Benadryl and other forms of diphenhydramine can also be used topically as a local anesthetic to reduce itching in dogs. In this case, using this medicine in cream or gel is also indicated. Apply to the area two to three times a day in this case.

Remember dosage will depend on the form of Benadryl prescribed by your vet and their own condition.

Benadryl for Dogs: Guide for Dosage, Side Effects and Safety - How much benadryl should I give a dog?

How long does benadryl take to work in dogs?

The effects of Benadryl will usually begin 30 minutes after your dog has taken it. When using this medicine to prevent motion sickness, you should give your dog this drug 20 minutes before the journey begins.

Gels will need to be left on the dog for 10 minutes if you are applying it while bathing your dog with shampoo for perfect results.

Side effects of benadryl in dogs

Apart from the contraindications mentioned above, even if your dog does not have any of those conditions, Benadryl has certain side effects that can manifest in your dog.

You may commonly notice your dog behaving in a strange manner, with slow reflexes. This is because the most common side effects of Benadryl are:

  • Drowsiness and sleepiness
  • Dry mouth (dog wants to drink lots of water)
  • Urinary retention
  • Sluggish or slow reactions

There are also less common symptoms that can occur in your dog but that can also be observed if you have given your dog Benadryl:

  • Diarrhea
  • Vomiting
  • Lack of appetite
  • Allergy (you should take your dog to the vet immediately if you notice symptoms of allergy)

Giving your dog a higher dose than what has been prescribed can put them in danger. If you have accidentally given your dog a higher dose you should take them to the vet immediately, especially if you notice the following symptoms:

  • Tremors
  • Rapid heartbeat
  • Breathing impairment
  • Fatigue
  • Confusion
  • Seizures
  • High temperature
Benadryl for Dogs: Guide for Dosage, Side Effects and Safety - Side effects of benadryl in dogs

Alternatives to benadryl for dogs

If your dog cannot take Benadryl or want a more natural alternative, you can also use other alternative medicines to treat your dog.

For example, if you are using Benadryl for anxiety in your dog, Anxietrex is a safe remedy that is free of side effects. Remember you should always use it under the vet's prescription.

On the other hand, you can use Derma-ionx for skin irritation and allergic reactions, as it does not have any side effects either. Derma-ionx for dogs is not available everywhere and it will work according to the dog's specific needs. if you are thinking of administering Derma-ionx for your dog, you should check with your veterinarian and always observe for any side effects.

If you do see side effects in your dog, but are unsure whether it is due to the allergy or a side effect, it is important to know the right symptoms of dogs. For this reason, we share this video on signs your dog is dying so you know when to react:

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Benadryl for Dogs: Guide for Dosage, Side Effects and Safety, we recommend you visit our Other health problems category.


  • Never give your dog Benadryl without consulting your vet beforehand

1. Food and Drug Administration. (2020). Approved Animal Drug Products (Green Book).

Write a comment
Add an image
Click to attach a photo related to your comment
What did you think of this article?
My female dog is in heat. My Male dog will not stop whining. How can I help him?
Bobbie Brenick
Cheyenne Anderson
gonna try baby benedryl for my 5lb chichuahua,he is a long hair and is constantly scratching....praying for relief for him
Administrador AnimalWised
We wish him well!
1 of 4
Benadryl for Dogs: Guide for Dosage, Side Effects and Safety