Comfortis® (Spinosad) is the first FDA-approved, chewable, beef-flavored tablet that kills fleas and prevents flea infestations on dogs for a full month. Convenient. Easy to give, with no messy applications Fast. Starts to kill fleas in 30 minutes — before they can lay eggs Effective. Provides full flea protection for a full month And Comfortis has been demonstrated to be safe for dogs and puppies 14 weeks and older.