Viagra (sildenafil) is mostly used to treat impotence. It does this by bringing more blood to the penis, which helps men get and keep an erection. Some men think that Viagra makes them last longer during sexual activity, but its main effect is on getting and keeping an erection, not on making the sexual encounter last longer. But some people may find that they can keep their erection longer after getting treatment for erectile dysfunction compared to when they didn't get treatment. It's important to know that Viagra doesn't directly change how long a sexual encounter lasts, and that its benefits are different for each person. To make sure safe and effective use, it's important to follow the directions your doctor gives you for taking Viagra and to tell them about any problems or concerns you have.