I have been using both Program and it's partner, Capstar, for over 10 years with fabulous results.  I found this flea medication after having 3 dogs infested with fleas from our neighborhood squirrels and raccoons.  I tried EVERYTHING short of flea bombing my house.  As a last ditch effort I used Capstar (immediate formula to kill existing fleas) and then the Program (monthly maintenance)and could not believe how fast it worked!  Seriously, not sure what happened to the one star reviewer except maybe they purchased some out of date product, because this stuff works - hands down.  When my vet asked me if I wanted to purchase Frontline for flea control and I told them I used Program and Capstar they could NOT argue with my choice!  Don't waste time and money on the other stuff that doesn't work, get control of the fleas on your animals right away the right way!!  No, I do not work for any of these companies, just very pleased and excited about the results of this product!