AF always arrives while I am still taking NPC, but I stop once she comes. I don't think this has as much to do with the NPC as it does the other supplements that I'm on, but I never get breakthrough spotting and I have been getting a nice four day flow.

On a side note, my GYN told me that NPC will not raise your progesterone levels to the same levels as those if you ovulate on your own, so I would recommend using other hormone regulating supplements in conjunction with the NPC.