Side Effects (Estrogenic):
Trenbolone is not aromatized by the body, and is not measurably estrogenic. It is of note, however, that this steroid displays significant binding affinity for the progesterone receptor (slightly stronger than progesterone itself).548 549 The side effects associated with progesterone are similar to those of estrogen, including negative feedback inhibition of testosterone production and enhanced rate of fat storage. Progestins also augment the stimulatory effect of estrogens on mammary tissue growth. There appears to be a strong synergy between these two hormones here, such that gynecomastia might even occur with the help of progestins, without excessive estrogen levels. The use of an anti-estrogen, which inhibits the estrogenic component of this disorder, is often sufficient to mitigate gynecomastia caused by progestational anabolic/androgenic steroids. Note that progestational side effects are more common when trenbolone is being taken with other aromatizable steroids.