Our Mikki was 4 months and 3.9 lbs. ans Minnie was 10 months and 3.5 lbs. when they first got the Comfortis pill. Both had no bad reaction at all and no flea ever since (1 1/2 months ago.) I give it to them with their main meal which is wet food (ground turkey with brown rice and blueberry yoghurt... no... they are NOT spoiled...
) Oh... and I use only 1/2 of the 5 to 10 lbs. pills...