Cystease S is cheaper than Cystaid. Cystease certainly helps my cat and I get them from VetUK. Between October and May my cat had five lots of cystitis. Throughout the summer I've put her on Cytease when we've been away a few times to prevent problems for catsitters and inbetween she's been on them once every three days, so I've gone nearly three months without a bout. Some cats are on a maintenance dose of one a day/one ever other day. I'm going to keep Lottie on one every three days to see if it helps. Like you, I can see no reason why my cat keeping getting it. I've changed to 100% wet cat food, have a Feliway diffuser and am trying to leave her to rest more.