I know that many natural-foods adherents do recommend kyolic garlic as a supplement for pets (cats or dogs) and that it acts to repel fleas. Because it is aged, the allicin is no longer present so it's not supposed to be harmful anymore. I used it in the powdered form sprinkled on canned food for all my cats awhile back, in small doses, and they thrived on it. I wanted an alternative to the usual flea-control chemicals. It's promoted as a tonic and systemic purifier as well.
Ironically, a year after I stopped giving them the garlic and gave in to using Advantage, Gollum did develop anemia owing to liver failure. He's a cardiomyopathy patient. But it wasn't garlic that caused it.
Regular garlic - especially fresh - is toxic to cats because of the allicin. Any member of this family - e.g. onion - will have similar components.
But it is best to get your vet's opinion on this subject.