a good otc wormer?

can i purchase a good wormer for an adult cat at a pet store?

Hello :)
   
So do you know what kind of worms your cat has?

Wormers may be parasite-specific. You don't know what to get if you don't know what the worm is.
   
Call the vet, make an appointment, & you'll need to bring a stool sample from that morning for them to look at under the microscope. It's worth the cost of the appointment, because worms can cause serious permanent health problems.
   
My cats had to be de-wormed, which involved several days of a specific drug that is NOT over-the-counter. (And it's actually not very expensive.)
   
After the cat's been de-wormed, put it on Revolution for Cats, which is the best preventive for pretty much every possible bug & parasite. Drs. Foster & Smith has a good price; most vets will price-match if you bring in a print-out from the website. Don't buy from 1-800-PetMeds & such, their sources can't be trusted. And most vets won't even let you buy prescription medicaiton online, they don't trust the sources.