I used it several years ago when my old pal Pumpkin, a tabby cat, was dying of kidney disease. He was 13 years old, and wanted to use the whole house for a litterbox. It didn't work on him, but it has on the 2 cats I now have. It worked quickly for the 2 cats, but maybe the disease my old cat had caused him to ignore it. Maybe that is your case too. I hope everything works out OK with Shadow. Good luck.......