Capstar is used as needed to kill adult fleas. It is not a preventative. A monthly flea preventative should be used to help avoid infestations. Capstar can be used in combination with monthly flea preventative treatments. No vet writer or qualified reviewer has received any compensation from the manufacturer of the medication as part of creating this article. All content contained in this article is sourced from public sources or the manufacturer. Featured Image: iStock/PhotoAttractive