honestly i dont know but i cant help but wonder if it has to do with the binding to the androgenic receptor site. Much like opiate blockers which bind to opiate recpetor sites but do not exert the opiate like effects. In other words im not sure the body can distinguish that its test or not binding to the androgen receptor...just that something has binded to receptor therefore causing or telling body levels of androgens are high therefore natural test production should cease. Total theory but makes some sense. Also would explain why high anabolic - low androgenic roids shut us down at a much slower rate.