Comfortis has demonstrated to be safe in healthy dogs and cats when used according to label directions. Use only for cats and kittens 14 weeks of age or older and 4.1 lbs of body weight or greater, and for dogs and puppies 14 weeks of age and older and 5.0 lbs of body weight or greater. The safe use of Comfortis in breeding, pregnant or lactating cats and dogs has not been evaluated.