Just to let you know, (as may of you will already know) this is what Jess is trialing at the moment, but it was released at the BSAVA conference on Friday so might now be available from vets,
In Jess's case we feel it is doing something as his calmer and has been weeing a bit more as a result.
Its not medicated its a protein based suppliment, so if you have a stressed/anxious (etc etc) cat it might be worth discussing with your vet if you want to try it.
It is also suitable for dogs (2 people at work are about to give it a go on their nervous dogs)
Anyway I thought I'd let you all know.