Clinical Endocrinology zyxwvut (198 1) zyxwvu 14, 49-6 1 zyxwvuts ANDROGEN REPLACEMENT WITH ORAL TESTOSTERONE UNDECANOATE IN HYPOGONADAL MEN: A DOUBLE BLIND CONTROLLED STUDY N. E. SKAKKEBAEK, J. BANCROFT, D. W. DAVIDSON AND PAMELA WARNER Laboratory of Reproductive Biology, University Department of Obstetrics and Gynaecology, Rigshospitalet and Herlev Hospital, Copenhagen, Denmark and M R C Reproductive Biology Unit, Centre for Reproductive Biology, Edinburgh (Received 21 February 1980; revised 30 June 1980; accepted zyxw I1 July 1980) SUMMARY The effects of androgen withdrawal and replacement were investigated in six hypergonadotrophic and six hypogonadotrophic men with hypogonadism. A double blind cross-over design was used comparing testosterone undecanoate (T.U., Organon International), 160 mg daily by mouth, with placebo. There was a significant effect of T.U. on all measures of sexual interest and behaviour. Sexual interest increased within the first week of T.U. administration, ejacula- tion usually returning within the second week. Behavioural responses were similar in the hyper- and hypogonadotrophic groups. The rise in plasma testosterone during T.U. administration was modest, not reaching the normal range in several cases. zyxw 5a dihydrotestosterone rose more substantially. There was a significant fall in sex hormone binding globulin, a rise in oestradiol and no significant change in gonadotrophin concentrations during T.U. administration. It is commonly assumed that the human male requires androgens for normal sexual behaviour. As with animals, castration in men has a variable effect, though predo- minantly a decline in sexual activity (Bremer, 1959; Tauber, 1940). Some men and animals, however, maintain a degree of sexual activity indefinitely after castration and without hormone replacement. It is therefore not clear to what extent androgens are necessary for human sexual behaviour, what components of sexuality are androgen- dependent, or what the time relationship is between androgen withdrawal and sexual decline. In neither hypergonadotrophic nor hypogonadotrophic forms of hypogonadism has there been any adequate controlled study of androgen therapy until recently. A dose- Correspondence: J. Bancroft, MRC Reproductive Biology Unit, Centre for Reproductive Biology, 37 Chalmers Street. Edinburgh ED3 9EW. 0300-0664/8l/OI004049$02.00 zyxwv 0 1981 Blackwell Scientific Publications 49