I've been on Coumadin for 24 years and the Coumadin has made my periods heavier than what's considered normal. They also lasted a little longer. I was 29 when I started on Coumadin. Now that I'm 53, I'm in perimenopause, and this definitely has been the worst. Just because of the fact that I'm in this time of my life, my periods are terribly heavy, irregular, and last about two weeks. My GYN says some of this is because of being perimenopausal, but we can also attribute a lot of it to the Coumadin. Anyway, hopefully, your daughter's periods will straightened out as far as regularity, but they may be a little heavier. And she has a long way to go until the menopausal stuff happens. Also, after my first OHS, my period was very irregular for a couple of months. I had always been like clock-work where that was concerned, but my doctors said that the stress of OHS can mess up your periods. Hope this has helped. Linda