tamoxifen

Can Tamoxifen mess with my cycle? In the last two months I have been spotting and having a heavy for 3 weeks at a time. I have always been "normal" 3-5 days max was my cycle. I have been on the Tamoxifen for little over 2 years. Would it take that long for the Tamoxifen to kick in? I have had other symptoms from the Tamoxifen right from the beginning, of taking the Tamoxifen. I'm normal when it comes to being at pre-menopause. My obgyn says she thinks it's from the Tamoxifen, but my oncologist says that the Tamoxifen should not effect my cycle at all. Can you shed some light on this.
Health Note: I've been taking the Tamoxifen becuase I'm at High Risk for BC. (I've been diagnosed with ADH, and have had 5 breast biopsies which all of them have come out benign).
Thank You, Rfrancis

[CCF-RN,MSN-rf]

Dear Rfrancis:  Although tamoxifen may interfere with normal
menstruation is some cases, it has also been associated with a slight increase in the incidence of endometrial (uterine) cancer.  As such, any abnormal vaginal bleeding while taking tamoxifen should be promptly evaluated by your gynecologist.