The effects of Cialis have been studied in men who have diabetes in addition to erectile dysfunction. These Cialis research studies also looked at the ability to achieve erections and the ability to maintain an erection after penetration. People took either Cialis 10 mg or Cialis 20 mg. Similar to the results of other Cialis studies, in people with diabetes, there were significant improvements in erections and successful intercourse attempts. For men with diabetes taking Cialis 10 mg, 57 percent had a satisfactory erection that allowed vaginal penetration and 48 percent had an erection that lasted long enough for successful intercourse. In those taking Cialis 20 mg, 54 percent had a satisfactory erection that allowed vaginal penetration and 42 percent had an erection that lasted long enough for successful intercourse.