Nolvadex is a known as an anti-estrogen, which help avoid gyno and costly gyno surgery. Nolvadex is an estrogen antagonist which prevents gyno by competing with estrogen at estrogen receptor sites. This prevents estrogen from entering receptors and creating estrogen activity. Since many steroids aromatize (change to estrogen) , the control of feminizing side effects is important. Males normally have low estrogen level. During steroid cycles estrogen levels can rise considerably, due to aromatization. Elevated estrogen level can cause side effects like increased fat deposits, water retention, and gynecomastia (growth of breast tissue and painful tumors underneath the nipple – also referred to as bitch tits). It is more the ratio of androgen to estrogen than just an increase in estrogen that triggers feminizing side effects.
Nolvadex does not decrease estrogen production. It blocks estrogen receptors. The sudden stopping of Nolvadex will allow increased levels of circulating estrogen to merge with the recently freed receptors and cause feminine reactions in the body (like gyno).

At the end of a steroid cycle, the body’s natural testosterone production is impaired. The aromatization of steroids estrogen levels are higher than normal and Nolvadex helps by blocking the estrogen receptors. If steroids are ended without regeneration of the HPTA under these conditions, much of muscle will disappear due to estrogen becoming the main hormone.