Stacking of steroids is a practice used that incorporates the administration of two or more steroids or illicit muscle building agents simultaneously. Stacking will often gradually increase the amount used over the course of weeks and then taper the use toward the end of the cycle (duration of time used). There are numerous reasons why bodybuilders stack drugs. The principal reason is probably effectiveness. Combining multiple drugs into the same stack often produces what’s called a synergistic effect. In simple terms this means that each drug in the stack magnifies or boosts the effectiveness of the others.