Capstar is a very effective flea control product. But unlike many other preventatives which last for 30 days, Capstar flea control only lasts for 24 hours. The active ingredient, nitenpyram, only kills adult fleas. However, this doesn't mean that the product isn't worth your money. One of the main benefits of using Capstar over other flea products is that it works very quickly. So quickly, in fact, that almost 100% of adult fleas on your pet are killed within 4-6 hours. Other products can take twice as long. This can be very useful if you're dealing with a severe flea infestation because fleas are able to reproduce very quickly. In just a short amount of time you can kill a lot of adult fleas before they are able to reproduce. Capstar can also be given to pets as young as 4 weeks of age, while other flea products require the pet to be either 6 or 8 weeks old. Because of this, Capstar is very popular with veterinarians, shelter groups, and rescue organizations that treat orphaned and stray puppies and kittens. Capstar is very effective at killing adult fleas, but for long term flea prevention and treatment it should be used in combination with other products such as Program, Sentinel, Revolution, or Frontline Plus.