Endometrial effects of etonogestrel (Implanon) contraceptive implant

The subdermal contraceptive implant etonogestrel (Implanon; NV Organon Inte rnational, Oss, The Netherlands) exerts complex effects on the endometrium. These include direct effects on the endometrium through endometrial proges tin target sites, and indirect effects through suppression of the hypothala mic-pituitary-ovarian axis. The resulting effects are categorized by altera tions in endometrial histology, endometrial thickness, dysmenorrhoea and me nstrual bleeding pattern. The exact mechanism of action of progestins on th e endometrium has not been determined. The contraceptive effect in Implanon users is mainly due to inhibition of ovulation. Current research is concen trating on the potential of the progestin implant to modify endometrial vas cular, angiogenic, steroid receptor and protooncogene function. These proce sses may be involved in the causation of progestin-induced breakthrough ble eding. Curr Opin Obstet Gynecol 13:335-341: (C) 2001 Lippincott Williams & Wilkins.