Research studies have also looked at the effectiveness of Levitra in people with diabetes. These studies investigated the ability to achieve erections and the ability to maintain an erection after penetration. People took either Levitra 10 mg or Levitra 20 mg. As in other studies, significant improvements were seen in erections and successful intercourse attempts. For men with diabetes taking Levitra 10 mg, 61 percent had a satisfactory erection that allowed vaginal penetration, and 49 percent had an erection that lasted long enough for successful intercourse. In those taking Levitra 20 mg, 64 percent had a satisfactory erection that allowed vaginal penetration, and 54 percent had an erection that lasted long enough for successful intercourse.