3-5 days. That's all it takes. Not 2-3 weeks like other testosterone boosters. In 3-5 days, Mass FX begins to work. Initially, you'll feel a rise in confidence. We call this the "alpha male" mentality. And it grows bigger each week. During your second week, you'll notice larger than normal improvements in strength compared to the week before. By day 12, your body will be producing almost 50% more testosterone. And, with improved aerobic power kicking in during week 3, Mass FX will help you exhaust your muscles even further, which forces them to get even bigger.