Tamoxifen is antiestrogen, produced for the reason of breast cancer in women because of high estrogenic amounts in there adipose tissues. For male athletes it was used for the primarily reason to stop the effect of conversion into estrogen causing gynecomastia. The structure of estrogen is very similar to testosterone, since it can aromatize many anabolic steroids is why the buildup of estrogens can be very serious concern. Estrogen can do two things negatively in males one is the extra build of fat, secondly being the extra water retention buildup in the it can increase production of FSH (follicle stimulating hormone) and LH (leutinizing hormone) in the male body. Activating the estrogen receptor can have a positive effect on HDL (good) cholesterol values.