Can you euthanize a dog with Benadryl?
You can euthanize the dog using sleeping pills, Benadryl, Tylenol pm. It is essential to select the perfect sleeping pills. Pentobarbital Sodium is the most effective anesthetic drug that can be chosen to euthanize your dog. The effect of the drug can be painful to the dog.

Reference:
How to Euthanize a Dog with Sleeping Pills, Benadryl, Tylenol pm ...
Dec 30, 2017