Some years ago there was an article in Mus. Dev. Mag. about this. I think it was titled "Are Anabolic Steroids Addictive"? The conclusion was that they are not addictive, but maintaining muscle mass was physchology addictive. You work hard and take these drugs to attain good muscle size and it is very difficult to lose back. But large muscle mass is hormone dependent and you can't keep this large muscle mass without using these hormones. One possible exception is guys 18 to 23. Their own hormone level is high enough and their genes help them keep this muscle mass for awhile. But sooner or later everyone loses back.