Our vet prescribes Valium. I forget the dosage.

He prescribes something for the cat too. grin

Of course you need to be able to cram the Valium down its throat without getting gouged. smirk

Or maybe they'll wolf it down in some tuna, or a Pill Pocket, Greenies makes them. See if the cat will eat the Pill Pocket before trying with a pill. If they do give some a few days before to establish a routine and sneak the Valium/Narcotics in one.

You might want to see how they react to the knock out pill, give it a test run.