Effects of estrogen treatment on sexual behavior in male-to-female transsexuals: experimental and clinical observations.

The effects of oral estrogen treatment on sexual physiology and behavior were examined in seven presurgical male-to-female transsexuals engaged in cross-living. Subjects were studied prior to hormone treatment, during long-term hormone treatment, and during an experimental double-blind period in which the effects of their usual hormone regimen were compared to those of placebo during successive 4-week periods. Subjects maintained daily logs of their spontaneous erections, sexual activity (masturbation), and feelings throughout the study. Nocturnal penile tumescence was measured, using home monitors, in order to estimate estrogen-induced changes in erectile capacity. Erectile response to sexually arousing stimuli (erotic films and self-generated fantasy) was also assessed in the laboratory. Blood samples were taken at intervals for testosterone and sex-hormone-binding globulin measurements and free testosterone levels were calculated. Estrogen treatment inhibited sexual activity, spontaneous erections, and nocturnal penile tumescence. No significant effects on psychophysiological response to film and fantasy or frequency of sexual feelings were found, but the psychophysiological data were very variable. Testosterone levels were suppressed by estrogen, but not to the extent that free testosterone levels were. It appears that declining free testosterone level is associated with inhibition of spontaneous erections (during both sleep and waking) and of sexual activity, though the latter relationship is less clear. No evidence of an effect on film or fantasy-induced erections was obtained.