Agree with with Felk....Its a receptor blocker strictly in the breast tissue. Although the only time you really need it if your prone to gyno like me and an AI doesnt do the trick fully. Although my gyno symptoms have decreased quit a bit as my bf % has dropped. I reduced my daily intake from 20mgs/daily along with 10mgs of Aromasin daily to 10mgs/daily (nolvadex). If your AI is doing the trick you do not need to take it during cycle. NOLVADEX is not an AI.