"Onions, garlic, chives, and leeks are in the Allium family, and are poisonous to both dogs and cats if the dose is right. Garlic is considered to be about five times as toxic as onions for cats and dogs. ... While minute amounts of these foods in some pets, especially dogs, may be safe, large ingestions can be very toxic."
Im no expert.
Personally i cant see the benefit of feeding garlic if toxic even in tablet form