Hi Shelagh - You don't say how old you are, but if you're under 50, it's not that uncommon for your period to return after an absence of many months. Arimidex won't prevent your period; it prevents estrogen from being converted into something useful to cancer cells. So I'd mention this to your doctor, and (s)he might be able to clear this up by doing some of those tests that tell you if you're peri-menopausal. Good luck - PJH
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