I have heard the debate, but I think common sense is needed when treating your dog with anything.....natural or not. Dogs are unique, just like people. Some dogs may not tolerate it well. Always keep a close watch on your furry friends. I can say that I have used garlic (one tiny piece of a clove for my 60 lbs border collie/lab mix about 4x a week with food). It cleared up her bad breath, never had a flea issue and she continued to check negative for worms. =) Just what has worked for me.