The active ingredient in Kamagra Gold 100 is sildenafil citrate. It belongs to a class of drugs known as PDE-5 inhibitors, which increase blood flow to the penis after sexual arousal. Sildenafil does this by blocking the enzyme responsible for the breakdown of cGMP. cGMP is a substance that relaxes and widens blood vessels and smooth muscle cells. This effect allows men to have a hard enough erection for sex.