I'm currently taking the GNC extended release 25mg. I only chose it based on the reviews on their website and haven't been taking it long enough to know how it works. One thing, I take it before bed and from day one I seem to wake up earlier than usual. I usually wake at 6:15, but the first time I took it I woke naturally at about 4:00 and every day since I've woke at 5:00. I've read recommendations to take it in the morning, but that doesn't work for me because of another drug interaction.