Tyler our cat has bean treated since may with Advantage but we had a sudden infestation last week so i ran to the grocery store and bought some Hartz Ultraguard. Thankfully he has had no negative side effects but Tyler still has fleas! Making it hard to treat the house because he keeps bringing them in. I am afraid to try another product for feat of a reaction with the Hartz. Going to try a Dawn bath after reading about it here. Poor little guy is being eaten alive :(. Bottom line… This Hartz crap doesn’t even work.