I've used Bitter Apple on Dusty (my cat) and my mom has used it on her cat Torry as well. No health problems from using it. The only problem I had with it was that Dusty was SO persistant with her obsessive licking, she'd just spit, drool, then lick again, repeat process until she had all the bitter apple licked off and could continue licking without the spitting and drooling. yuck!