It is an antidepressant of the original type, tricyclic, Brand name Elavil. It also helps relieve anxiety, and also can help with migraine headaches.
Dogs can have benadryl but please call your vet first
it is barbiturate
benzodiazepines
It can be, though frankly if your cat is so freaked out by grooming that it requires a sedative, it's probably better to let it handle its own grooming. Cats are by nature fairly clean animals.