Sizegenix is a male enhancement supplement that is designed to improve sexual performance. The active ingredient in Sizegenix is L-Arginine, an amino acid that is essential for the production of nitric oxide. Nitric oxide is responsible for relaxing blood vessels and increasing blood flow, which can lead to improved erections. In addition to L-Arginine, Sizegenix also contains Tribulus Terrestris, a natural herb that has been shown to increase testosterone levels.