Yes, my cat Mr Grey who has allergy/immune issues is currently taking this to help improve his appetite. It seems to be helpful, he's up to 8 pounds now (he was 9 before he got sick, and down to 7-something before the med.)
The transdermal form has worked very well for us in several different situations.
I would not recommend the tablet form as even a very small amount can cause dry mouth.
I appreciate the replies. Actually, I'm going to be getting the cyproheptadine compounded into a liquid form that will be administered by syringe. That's how I do the methimazole as well. Hopefully it'll get her to eat a bit more. Her weight is hanging between 7-8 pounds but recently closer to 7. Most of her life she was a 9-lb. cat.