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.
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.
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.
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.
What to Do If Your Dog Overdoses on Benadryl
If you suspect that your dog may have eaten any Benadryl, or if you think you may have accidentally given too much, contact your veterinarian or an emergency veterinary clinic immediately. You could also consider calling Pet Poison Helpline at 855-764-7661 or ASPCA Animal Poison Control at (888) 426-4435. They can help you determine whether your dog may have consumed a dangerous amount, and what to do next, for a reasonable fee.
Symptoms of Benadryl Poisoning in Dogs
Although Benadryl is generally safe for dogs, some side effects can occur. Side effects usually occur within an hour of administration. They are typically mild and can include:
Overdoses of Benadryl are more often caused by your animal getting a box of the medication from the garbage or medicine cabinet than by being given too much. If you see these signs of an overdose, contact your veterinarian immediately.
Types
Along with a version of diphenhydramine by the name of Vetadryl developed specifically for cats and dogs, there are a few other first generation antihistamines that can be used for dogs. These can include:
Chlorpheniramine – This antihistamine is frequently used in small animal veterinary practice and is less likely to cause drowsiness than some of the others
Clemastine – Clemastine is classified as an antipruritic (anti-itch), as well as a sedating antihistamine, and is tends to exhibit fewer side effects
Hydroxyzine – This drug is a more aggressive antihistamine, but also has more potent side effects
Meclizine – Commonly used to reduce nausea, particularly nausea caused by motion sickness