Capstar tablets are used to kill adult fleas on dogs and cats weighing 2-25 lbs. , begins working in 30 minutes. Comes with 6 tablets. Active ingredient is nitenpyram. For cats and dogs 4 weeks of age or older and weighing at least 2 lbs. or more. Recommend using a topical monthly flea treatment with this product. Check out our flea control kits for the best savings.