Groucho is an only cat and fortunately he doesn't vomit very often. I did call our vet about it once because I didn't notice anything hairball related. It was a milky colored fluid and food. Our vet said it WAS hairball and recommended putting vaseline on his upper lip. As he would try to clean it off, he'd swallow it. Once in his system the vaseline would keep things moving. Our vet also said hairball treatments are just flavored vaseline. It works for us.