Fleas can be a source of great suffering for your cat or your dog. Fleas can cause constant itching, pain (from biting again and again), and if swallowed, fleas can cause tapeworms. To prevent a flea infestation: fleas spreading to other pets, people, or your home, you should start a flea treatment as soon as possible. Capstar for cats and dogs is a fast-acting, effective treatment that starts killing fleas in 30 min and kills 90% of them within hours. Capstar is an easy to administer tablet that can be given daily to dogs, cats, puppies, and kitten older than four weeks and more than 2.2 pounds.