INVITED COMMENTARY Reappraisal of progestins in endometriosis therapy

Endocrine treatment of endometriosis is based upon the suggestion of Kistner that regression of endometriosis can be obtained by induction of pseudo-pregnancy with a combination of oestrogen and progestin (1). The 40-year history of conservative medical therapy of endometriosis demonstrates that many substances and their combinations have been tested, including low-dose oral contraceptives, progestin alone (several candidates), danazol, gestrinone and gonadotrophin-releasing hor-mone (GnRH) agonist analogues (2, 3). Unfortunately, the clinical efficacy of different treatment modalities was investigated mostly retrospectively or in uncontrolled trials until the late 1980s (2, 3). The more recent studies on the efficacy of drug therapy have been prospective and based on adequate study designs with control therapy