That was my concern as well, and I was expecting to feel jittery and nauseous when I tried it (because all diet supplements do that to me), but not at all. It's all natural and although it contains some caffeine, it's not nearly
enough to make your heart race or get the jitters. It's thermogenic. You can read about it on their website: OxyELITE Pro - The USP Labs Fat Burner That's MELTING the Market: $27
ETA: It kick-started my diet and I lost a lot of water weight.