Arimidex works differently from SERM’s. Instead of blocking the receptors for estrogen it blocks the conversion of aromatizable steroids to estrogen. In this way it eliminates estrogen from the users body. In fact it often eliminates estrogen too well. If you are going to use Arimidex for longer than 1 week I recommend that you monitor your blood estrogen level to determine proper dosing. You don’t want to completely eliminate estrogen, just reduce it.