This question applies to anyone currently taking anastrozole (tradename Arimidex). The research on anastrozole clearly shows that anastrozole inhibits the CYP3A4 class of liver enzyme. Just a little background, CYP3A4 is the primary complex involved in the metabolism of xeno compounds(synthetically produced compounds, not found in nature).
I have found that even while taking a smallish dose of less than .5mg per week, even a cup of coffee seems to give me a bit more rev, and desired effects are much more pervasive and long lasting.
I am fully aware of the possibility that the two events are non-related, but the science does "in theory" reveal a link between increased duration of biological effects of various xenogenic compounds due to co-administration of CYP3A4 inhibitors (in this case, anastrozole).
I am too lazy right now to look up the studies, but if you just perform the google search "CYP3A4 inhibitor anastrozole" that will take you to the source.