Lethal Dose of Benadryl for Dogs & Overdose Risks

This article was updated on November 12th, 2022

On top of the emotional stress following illness and vet treatments, many dog owners also face expensive vet bills. As a result, many owners are trying to find inexpensive options to euthanize their dogs, and want to figure out how to euthanize a dog with a simple over-the-counter product such as Benadryl, and what to find out what the lethal dose of Benadryl is for dogs.

While Benadryl can indeed be lethal to dogs, there are several very important legal and medical factors that you should consider. Benadryl is generally a terrible (and illegal) way to euthanize dogs, and we will offer several better alternatives in this article.

Lethal Dose for Dogs

According to this scientific paper, the lethal dose for diphenhydramine in dogs ranges between 24 to 30 mg per kilogram of body weight by IV administration. For a 40-pound dog, this would equate to about 430 to 540 mg, or 9-10 tablets (for tablets with 50mg diphenhydramine – note that some tablets are 25mg only). However, it is essential to note that this study was very limited in scope, and estimates are derived from extrapolated values from other species. What do we take from this? The lethal dose of Benadryl for dogs is still largely unknown. Let’s review other critical considerations.

Overdose Risks

Dogs can overdose on Benadryl if the dose given is too high. Merck recommends 2-4 milligrams of Benadryl per kilogram of body weight. Exceeding this dose can cause dramatic side effects, including excitability, rapid heartbeat, seizures, convulsions, or respiratory failure. The exact dosage that could cause an overdose in dogs is not known and will depend on the dog. It is not recommended, and most often simply illegal, to use Benadryl to euthanize a pet.

Critical Considerations About Benadryl’s Lethal Dose & Overdose Risks

There are critical reasons why Benadryl should NOT be used to put your dog to sleep, including the following:

1. Benadryl will create unnecessary suffering for your dog.
   Benadryl is lethal to dogs because it can cause serious neurological and cardiovascular effects, with effects including hyper-excitability, rapid heartbeat, seizures, convulsions, or respiratory failure. This will result in a very painful death for your dog. There are much more humane ways to euthanize your dog, as we explain below.
   
2. Most vets will ensure that your dogs are sedated prior to euthanasia, creating a pain-free experience.
   Your veterinarian will make sure that your dog is sedated and will not experience any pain prior to receiving the euthanasia medication.
   
3. Most US states require that a veterinarian performs the procedure. Dog euthanasia in the US is highly regulated and can ONLY be performed by a veterinarian professional or euthanasia technician in most cases – this is to ensure a pain-free and effective process for the animals.

If you are looking for an inexpensive way to euthanize your dog, we have several options. Read our article How Much It Costs to Put a Dog Down [Estimates Included] which offers several low-cost alternatives and ideas directly from our veterinarians.

To learn more about Benadryl overdose risks for dogs, read our other article: Euthanizing a Dog at Home With Benadryl? Risks & Recommendations.