There is always OTC medicine. It's the route I went when the vets couldn't come back with a response that he had worms. I knew he did, I saw he did and yet the vets did not.

Pet stores sell them and they usually come in capsule form. Make sure to follow the directions (obviously) if that's the route you decide to go. In the end it worked and he didn't have worms anymore.

I will say that it should be a last resort and if you aren't sure what specific type of worm your cat has, try to get one that covers as many as possible.