Cobra Generic is one of the most well-known drugs in the world, used to treat erectile dysfunction, or ED, and impotence. Sildenafil is the active ingredient in Cobra Generic. It relaxes muscles and blood vessels in the penis for better blood flow, making it easier for a man to develop an erection. Take Cobra Generic within 60 minutes of sexual activity to make it easier to become erect. Note that common side effects include temporary changes in vision and flushing.