Most commonly called Arimidex, this substance is a true aromatase inhibitor which works by blocking the aromatase enzyme in the body, thus limiting the amount of estrogen buildup that takes place. This compound has obvious benefits to bodybuilders who use aromatizing steroids such as testosterone. These individuals might face estrogen related side effects such as water bloat and "gyno", but by taking GP Anastrozole while on cycle, the chance of any of these sides are greatly reduced.

In studies that have been done, Arimidex has been shown to reduce estrogen in the body by roughly 50%. This is a good balance for bodybuilders , because some estrogen is needed in order for the full anabolic benefits of the steroids being taken to be achieved. These results are typically the same with a dosage of .5 mg a day as they are with a dosage of 1 mg a day, meaning that in most cases, a half tablet a day will be sufficient for estrogen control throughout cycle.