My vet offered to put Sugar on it when her back end problems caused incontinence, but I said, with all her other health problems, I'd rather just clean up after her. I know many people have used it with no problems, but like Heather said, you need to be aware of the side effects.
I am glad he's off since he was showing a reaction. FWIW, once Sugar's back end got better, the incontinence mostly stopped. Acupuncture helped with that.