Training twice a day (or more) has been a very successful protocol for many, many men, including very top level athletes. The trick is not to make any one workout overwhelming hard, that recovery is slowed or stopped all together. The CNS needs to be stimulated, but not over taxed. On any rep, of any set, the point of failure (either momentary, temporary or complete) is never approached. Usually staying at least 2 reps away from any of those points. These workouts are kept brief and to the point. Want to encourage muscle/strength growth and not try to force it.
Can train the same body part or opposite body parts twice within a single day. Though some find favor with working the same body part that day. Like benches in the morning and dips or inclines in the afternoon (remembering to never approach the point of failure). Olympic lifters have been known to train 3 to 4 times in a single day. I have heard of 5 times a day, but can't confirm that.
From personal experience, when in college and doing off season weight training, we all did twice a days in the weight room. And with exceptional results, in muscle and strength gains. Some of the best gains of my life. Good Luck
Side Bar: Never a drastic need for drugs if you use common sense and have a workable knowledge of your training and how the body reacts to certain methods of training. If your just lifting heavy stuff without any specif plan of how to workout, your just wasting time.
