Certifect for Dogs 23-44 lbs - 6 Month Supply Certifect for dogs and puppies 8 weeks or older and 23-44 pounds. Certifect for dogs rapidly starts killing ticks within 6 hours providing a convenient, effective treatment for all stages of ticks. Certifect kills fleas, flea eggs, flea larvae, prevents the development of all stages of fleas and kills chewing lice, and all stages of ticks. Certifect can be used on breeding, pregnant and nursing dogs. Certifect is only for dogs, but no adverse effects were seen in cats sharing households with treated dogs.