How Much Benadryl Is Fatal For A Dog?

Benadryl is a medication commonly prescribed for allergies and other conditions. In some instances, however, it can cause serious side effects in dogs. How much should you give your pet?

Benadryl is a drug that relieves symptoms of allergic reactions such as sneezing, runny nose, watery eyes, and itching. The recommended dose varies from person to person depending on their age, health condition, and body size.

How Much Benadryl Is Fatal For A Dog

While the amount of Benadryl needed to treat an allergy or other medical condition depends on the individual, there is a safe maximum dosage for dogs. This should not be exceeded to prevent fatalities in pets.

Today we are going to be looking at how much Benadryl is fatal for dogs.

General Dose Of Benadryl For Dogs

The general dose of Benadryl for dogs is usually between 2 and 4 mg per kilogram of dog’s weight.
This means that if your dog weighs 12 kg then he would need between 24-48 mg of Benadryl.

This dose can be given up to three times a day. However, we would suggest only using it when you really need to and your dog is showing clear signs of distress. It is better not to use Benadryl as just a precaution to prevent an accidental overdose.

How Much Benadryl Is Too Much For Dogs?

The amount of Benadryl it would take to kill a dog would depend on its weight and other external factors. However, as a rule of thumb, 2.5 tabs of Benadryl is considered the maximum dosage that a dog can withstand.

Look out for adverse side effects such as vomiting, diarrhea, rapid heart rate, and fast breathing. If your dog is experiencing any of these then you should contact your veterinarian immediately for professional help.

Can Dogs Overdose On Benadryl?

Yes! As mentioned earlier, the amount of Benadryl required to treat an allergy or another medical condition will vary slightly from dog to dog. Therefore, it is possible for a dog to overdose with this allergy medication.

As a precaution, never give your dog too much Benadryl. We would suggest working up to the maximum dose rather than giving it to them outright.

For example, give your dog half of the maximum dosage and allow it to kick in before determining whether they need the rest of it or not.

Some dogs will feel much better on half a dose, and others might need more Benadryl to feel like themselves again. Still, it offers less chance of overdose by working up to the maximum dose rather than giving it all to them at once.

Always contact your veterinarian if you are unsure of what dose to give your dog. It is always better to be safe than to be sorry. Benadryl overdose can lead to diphenhydramine poisoning, which can be fatal.

Signs Of A Benadryl Overdose In Dogs

If your dog has taken too much Benadryl, you may notice one or more of the following:

  • Vomiting
  • Diarrhea
  • Rapid heartbeat
  • Fast breathing
  • Drowsiness
  • Lethargy
  • Mental confusion
  • Constipation
  • Agitation
  • Dilated pupils
  • Seizures

Your dog might be exhibiting different symptoms depending on how much of an overdose they took.

For example, slightly too much Benadryl might just lead to diarrhea and vomiting, while a dangerous overdose could exhibit seizures and constipation as symptoms.

Nevertheless, all overdoses are dangerous for your dog and should be checked out by a veterinarian immediately.

How Much Benadryl Can A 50 Pound Dog Have?

A 50 pound dog weighs 22.67 kilograms. Taking what we said earlier about dogs being able to have 2 to 4 mg per kg, we can work out what a 50 pound dog is allowed to take.

How Much Benadryl Is Fatal For A Dog (1)

If your dog weighs 50 pounds then the maximum dose of Benadryl that they can take is 45.34 to 90.68 mg. They can have this three times a day maximum.

Talk to your veterinarian if you’re worried about giving your dog Benadryl for the first time. Many suggest giving them a smaller dose in case that is all they need.

How Much Benadryl Can A 100 Pound Dog Have?

Similarly to the above section, we can take the fact that dogs can have 2 to 4 mg of Benadryl for every kg of their bodyweight and work out how much is their maximum dose.

A 100 pound dog weighs 45.36 kg. This means that the maximum dose that they are allowed is between 91.26 and 181.44 mg. Again, they can have this dose three times a day.

When Does Benadryl Leave A Dog’s System?

Benadryl stays in the body until it is removed by the liver. The liver takes some time to remove the drug, so it can stay in the system for around 24 hours after ingestion.

This means that when your dog ingests Benadryl, it will begin to act within 30 minutes. However, it won’t start to leave their system until around 24 hours later.

This also means that if your dog ingests Benadryl, they will probably still feel its effects even though they took it several hours ago.

It’s also worth noting that if your dog has liver or kidney disease, then the drug can stay in their system for longer.

When Does Benadryl Kick In?

The effect of Benadryl kicks in almost instantly. Within 10 to 15 minutes of taking the drug, your dog will start feeling sleepy.

The peak effectiveness is between 1 and 2 hours of taking it, so after this you might see the drug begin to wear off.

How Many Milligrams Are In A Benadryl Tablet?

There are varying strengths of Benadryl tablets available; however, the most common strength is 25 mg per tablet.

You can also get Benadryl tablets in 50 mg form. Make sure that you know which Benadryl strength tablets you have so that you don’t accidentally go over the safe limit for your dog.

If your dog’s weight means that their maximum dosage is an uncommon number, don’t exceed their maximum dose allowance.

For example, if your 50 pound dog’s maximum dosage was 90.68 mg, do not give them two 50 mg Benadryl tablets as it’s ‘close enough’. Give them either one 50 mg tablet, or give them one and a half. This will ensure that you are safely below the maximum dose and prevent you from accidentally overdosing your dog.

What To Do If You Give Your Dog Too Much Benadryl

If your dog eats too many Benadryl tablets, they may become sick. It’s important to talk to your veterinarian immediately. They might tell you to take your dog to the emergency veterinary hospital.

If you think that you have given your dog too much Benadryl, or something is not right with your dog, contact a vet quickly.


Benadryl can be fatal for dogs when they are given a dose more than their body weight allows. For every kilogram of weight, your dog can withstand between 2 and 4 milligrams of Benadryl.

Most people will advise you to use a lower dose of Benadryl for your dog at first before moving onto the maximum dose.

If you have given your dog too much Benadryl, contact a veterinarian immediately. Similarly, if you have any questions regarding giving your dog Benadryl, talk to a professional beforehand.

Megan Turner