It works well. The main things I have found with Program is that it takes awhile to get into the system. You won't see immediate results here. It really kicked in good on the 3 to 4 month and from that point on no more eggs, larva or baby fleas. The other thing is it must remain in their blood stream so it has to be given every 30 days. For it to work right you have to kind of commit yourself to using it on a regular basis for the long  haul . I think it is worth doing. It does work very well at what it does