Our Mr Miyagi had an issue with constipation a couple years back (or so). We've had really good success with feeding only canned food (Natural Balance Duck and Green Pea - he doesn't seem to tolerate any others). He's also on 5 mg of cisapride per day (it just helps keep things moving along). The vet has suggested we try and wean him off of it, but given we have two cats, it's sometimes difficult to tell who is doing what in the box
There is no harm in having it, so we'll just keep on it