Although they didn't shrink, my breasts were noticeably less tender when I stopped PIO (and all other meds at 12 weeks). Could have been PIO, could have been getting past the 12 week mark, not sure. I didn't sleep as well without the help of the progesterone. I also got a few headaches at night for about a week - likely from the estrogen withdrawl. I should mention that although my breasts were less tender, the nipples have remained sensitive as ever!