Kamagra 100 (Sildenafil 100mg) is a generic version of popular branded medicines that belong to a group called PDE5 inhibitors. It works by relaxing the blood vessels in your penis. This allows blood to flow into the penis and produce an erection when sexually aroused. This medicine will only help get an erection if you are sexually stimulated. It is very effective but needs to be taken at least 30 minutes before sexual activity.