Guardian One Flea Monthly Prevention Capsules for Dogs 10-20lbs contain Nitenpyram, which begins working within 30 minutes, and Lufenuron, which provides protection for 30 days. These two ingredients are the gold standard in pet supply products and have been proven to be both gentle and effective. Unlike other products, Guardian does not use preservatives or artificial flavors, instead opting for all-natural, restaurant-quality cuts of meat. The meat is then preserved using only oak or hickory-fired smoke, giving it a shelf life of almost indefinitely refrigerated and 2 years or longer in a room temperature drawer. The airtight bottle cap and gelcaps locking design ensures minimal air penetration, making it more effective than traditional tablets or soft chews.