Prohormones in the broadest sense is anything with a hormonal action that converts into something else that is presumably active. All hormones are really prohormones to something else, because the amount of interconversion between hormonal agents is nearly endless. When a steroid is relatively weak on it’s own or has no activity it is called a “prohormone” when an androgen is active on its own it is typically called anabolic steroids. This is what separates a prohormone from an “anabolic steroid”. Andro Cycles - Androstenedione Information and Effects, Andro Information. http://www.androcycle.com/