The hormonal profile of norethindrone acetate: rationale for add-back therapy with gonadotropin-releasing hormone agonists in women with endometriosis.

Gonadotropin-releasing hormone agonists (GnRHa) are an effective treatment of endometriosis-associated pelvic pain. The use of hormonal add-back therapy can alleviate the hypoestrogenic symptoms associated with GnRHa therapy, while preserving therapeutic efficacy. Norethindrone acetate (NETA) is a unique progestin that has both estrogenic and androgenic properties and is effective as an add-back regimen without estrogen supplementation. Through its estrogenic activity, NETA exerts beneficial effects on bone mineral density and vasomotor symptoms in women treated with GnRHa. In addition, NETA exhibits strong endometrial antiproliferative effects, which may result in further benefits for the endometriosis patient population. However, NETA add-back may be associated with progestogenic side effects and may lower high-density lipoprotein due to androgenic activity. These effects must be balanced with the overall benefits of NETA add-back therapy.