My elderly cat suffered from extreme constipation. She would strain and nothing would pass. I found two things that worked well. Canned pumpkin - 1/2 teaspoon each day. It takes a couple of days to work through the system, but it did the trick. Also, my holistic vet recommended slippery elm. I opened a capsule and put about 1/4 capsule in some liquid, dissolved it, then gave it in a syringe. This also worked very well.