I started taking this years ago when a workout partner recommended it to me at the gym. He said he hasn't had a cold or felt run down, since using it. It was great for me because I work in an emergency room and I am around sick people all day long. While all my coworkers were coming down with colds and flu, I stayed healthy! I recommended it to everyone and they haven't looked back. It's also great for an energy boost or as a replenishment after a hard workout. I like the orange flavor and tangerine, the best. They used to have cola flavor, which wasn't bad, but I see the have stopped making it.