How To Euthanasia A Cat With Over The Counter Drugs. Pentobarbital is now most commonly used for euthanasia for dogs and cats. Cats are sensitive to some medications, one of which being aspirin.
One can either use the oral barbiturates or even give an injection. This dose will put your cat to sleep slowly and peacefully. Such a dose of benadryl will put your cat to comma in a few minutes after which it dies peacefully.