How Much Benadryl Can I Give My Dog?


Dogs are wonderfully curious, energetic creatures. But even the most loyal of these four-legged companions can sometimes make some bad choices, and end up in a situation that they probably shouldn’t. Sometimes it’s running through poison ivy, or getting stung by a bee. There are a lot of different circumstances that might lead your dog to have some kind of allergic reaction. 

Whether they end up itchy, uncomfortable or even swollen, you want to be able to make your pooch feel better. But if you can avoid going to the vets, that’s going to be preferable. Now, you certainly want to call a vet, just to make sure that it’s not serious. With their guidance, you should be able to give your dog some Benadryl and get him back up on his feet in time. 

Here is a brief guide to how much Benadryl you should give to your dog, but always make sure that you check with your vet first that it’s okay, and if you’re unsure about how much even after you’ve read this, please make sure you call a professional, rather than guess. 

How Much Benadryl Can I Give My Dog?

Table of Contents

What Is Benadryl?

Benadryl, or diphenhydramine, is an antihistamine that helps relieve symptoms of allergic reactions in humans, as well as in animals. It can also be used to help alleviate motion sickness in dogs if you need to take them on a long trip.

However, it can also sometimes have the opposite affect. So you should never give you pet medicine like this without talking to your vet first. 

For the majority of dogs, Benadryl is going to be perfectly safe. It’ll relieve their swelling or rashes in just a couple of hours. But getting the dosage right is important. Dogs are generally a lot smaller than humans, and therefore need a lot less than a grown human.

Dogs also metabolize Benadryl at a different rate and in a different way. So generally it’s just a good idea to ignore the human guidelines when it comes to giving this medicine to your dog. 

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Benadryl Dosage Based On Size

The correct dosage of diphenhydramine for dogs depends mostly on their weight. Therefore, a small dog is going to need a significantly smaller dose of medication than a big dog to get the same positive results. 

The generally agreed upon amount is about 2mg of medication per kilogram of weight. This amount can be administered two to three times daily if needed, but don’t go above three does in 24 hours.

So for example, if your dog weighs 25lbs (11.3kg) the does of Benadryl would be 22.6mg, but could be upped to 25 to make it easier, as Benadryl tablets are available in 25mg versions. 

It’s definitely best to only give your pet vet-approved Benadryl tablets or ointments, but there are some cases in which it’s possible to give them tablets that have been intended for humans.

However there are some pretty important things to keep in mind if you’re going to do that. 

If Using Human Tablets, Keep This In Mind

First of all, you must make sure that you’re giving your dog a tablet that has only diphenhydramine in it, and no other active ingredients.

Never give your dog anything that has decongestants or alcohol in it. These can be seriously toxic to your furry pal. 

Next, you’ll need to avoid slow-release capsules. Dog’s stomachs work differently to a human’s. A capsule that would work well for us, isn’t going to work well for a dog.

Plus, if your dog happens to bite the capsule on the way down, they’ll get the whole dosage at the same time, rather than slowly, which could be an overdose. 

For small dogs, it’s probably going to be best to use children’s Benadryl than Benadryl for adults, which would let you adjust the dose more carefully and not give your dog too much. 

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Risks Of Giving Your Dog Benadryl

Whilst the right dose of dose of Benadryl should be safe for the majority of dogs, it is possible that they could be allergic to the medication itself.

An allergy to diphenhydramine will have similar symptoms to other allergies, depending on the severity. These reactions could include:

  • Swelling of the face or tongue
  • Diarrhea, vomiting, upset stomach
  • Skin Chewing/licking
  • Red Rashes on skin

Any symptom should be noticeable within the first hour after giving the medication, so keep an eye on your dog in case there are any changes.

If you do see signs of an allergic reaction, call your vet immediately. 

Risks Of Giving Your Dog Benedryl

Other Side Effects

There are other, milder symptoms that your dog may experience, similar to what you may experience as a human. These include:

  • Sleepiness
  • Dry mouth
  • Rapid breathing
  • Hypersalivation 
  • Increased heart-rate

Generally these side effects should be fine, but again, just keep a close eye on your dog to make sure that they’re healthy. 

The most important thing that you want to make sure you’re aware of is a Benadryl overdose.

Ignoring any of the guidelines laid out here could result in your dog overdosing, which could lead to seizures, respiratory failure, or even a coma, depending on how much of an overdose they have experienced. 

If you believe that your dog may have overdosed, you need to call your vet immediately. 

How Much Benadryl Can I Give My Dog? – The Bottom Line

So long as you consult your veterinarian, giving your dog vet-approved Benadryl shouldn’t cause any issues. However you do want to make sure that you give them the correct dosage, and don’t give them too much. 


What does too much Benadryl do to a dog?

One of the common side effects of Benadryl is sedation. While this can be useful for calming anxious dogs or helping them sleep during travel, excessive sedation can make your dog lethargic or excessively drowsy. Always consult your veterinarian before giving any medication to your dog, including over-the-counter options like Benadryl.

How long does Benadryl last in dogs?

The effects of Benadryl typically last for about 4 to 8 hours in dogs.

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