We used it last summer with Colonel, and it was great! He didn't like eating it on his dry food, so we would put some plain yogurt on his food, and sprinkle the Angel Eyes on that. In the winter time, his environmental allergies die down and he doesn't have a tear stain issue so we only used it last summer. We have since kept giving him just plain Yogurt, which has not eliminated tear stains so I know the Angel Eyes are what did it. Our vet said she does not recommend it because one of the ingredients is a hormone that she doesn't like, but I don't know of any other products out there that help like Angel Eyes do! No bad side effects or anything on our end. But I would be interested in hearing other options to avoid the hormones! Colonel's stains are pretty bad this summer and we have been cleaning them with diluted peroxide, which only works for about a day.