"This product is tricky. Since it is caffeine your heart may race, it took me a week to adjust how much to take. One tablet made my body feel restless and tired at the same time, a very irritable feeling. I would not drink any other products containing caffeine with this one. I switched to half a tablet and was able to attack my exercises. I only take this before working out early in the morning. Eventually your body will adjust so it's a good idea to use this temporarily. Overall, this product does what it offers."