Arimidex (Anastrozole) is what we call an aromatase inhibitor (AI). In clinical use, it´s used to halt the progression of Breast Cancer in women. It works by blocking the aromatase enzyme, which is responsible for the production of estrogen. In athletics and bodybuilding, it is used as an ancillary compound to be added to a cycle of Anabolic Steroids. In this respect it is also used for its estrogen reducing properties, but it has the additional benefit of increasing testosterone levels, as we´ll see...

Arimidex Side Effects

Many anabolic steroids aromatize (convert to estrogen via the aromatase enzyme), and this is responsible for many of the unwanted side effects found with anabolic steroid use (acne, gynocomastia, water-retention, etc...). In one study, both .5mg and 1mg doses of Arimidex were shown to decrease estrogen by roughly 50%. The 1mg/day dose also increased testosterone levels by 58% (1). In that same study, in both groups, LH and FSH also went up slightly.

Arimidex and Cholestrol

Lowered estrogen levels could possibly (eventually) adversely affect your cholesterol and possibly even your immune function.This should be the ancillary compound of choice for those on long and heavy cycles, especially since it also doesn´t inhibit igf like some other ancillary compounds (insulin-like-growth-factor is an important component of anabolism)(4).

Source: steroid.com