My 1 year old male DLH cat was just treated for tapeworm about a week ago. They gave him his medication at the vet office and the stool sample came back negative for parasites. We put him on the Revolution prescribed by our vet and now he has diarrhea. He drinks and eats properly. Are there any over the counter medications to try or is it necessary to go back to the vet?

Hello, Tapeworms are a frustrating parasite because we frequently miss them on a fecal sample and rely on you to tell us you see them. With most other parasites we visualize the eggs under the microscope. With tapeworms, all the eggs pass in those little white segments. Therefore we will treat based on your observation, and institute flea control since swallowing an infected flea is how the cat gets infected. As far as the diarrhea…..There is a long list of causes. You alluded to intestinal parasites and the negative fecal results.  Absolutely, intestinal parasites can cause diarrhea – some of which do not show up on every fecal (especially if the sample was small). Other causes for diarrhea include: side effect of medication such as droncit (tapeworm medication), revolution; eating inappropriate food; stress; ingedient sensitivity in cat food; infections (viruses, bacteria); etc. I did mention that the medication prescribed may play a role in diarrhea – although rare.  The treatment provided certainly sounds very appropriate. If the diarrhea persists, your cat does need to be evaluated and may need additional tests performed, or perhaps a diet change.  Diarrhea can be a frustrating problem in a cat and there is no over-the-counter fix that can be recommended without examing your cat first.  I hope this information is helpful. Sincerely,  Christine Simon D.V.M.