Peta - i've been having antagonist cycles (cetrotide) and what it does is baically similar to lucrin/synarel in that it stops production of your own hormones - just for a much shorter time - so in the case of a stim cycle, when you get follies that aren't quite ripe wnough for the picking, they use the cetrotide to stop the surge of LH that would naturally cause you to O - they basically just use it to make sure that O is when they want, not when your body wants it! hope that isn't too jumbled or confused - have 2 cats and 4 dogs vying for my attention cos i just got home from work!!