Adenomyosis is a benign uterine disease which causes disturbing symptoms for premenopausal women. The common two symptoms are dysmenorrhea and heavy menstrual bleeding which can be severe and impair quality of life. The etiology of adenomyosis is suspected from the endometrial gland and stromal that invade uterine myometrium which cause pain symptom and heavy bleeding on menstruation.

Dienogest is the fourth generation of oral progestogen which can cause endometrial decidualization and atrophy. Several previous studies stated that continuous regimen of dienogest was efficacious to treat adenomyosis in terms of reducing dysmenorrhea and heavy menstrual bleeding. However, dienogest has also been shown to have high undesirable side effects. Irregular bleeding or spotting is the main side effect which can be found in more than half of the patients and leads to discontinuation of treatment.

Cyclic regimen of dienogest, 3-week period with 1-week withdrawal period, to reduce irregular bleeding during treatment of endometriosis was evaluated. It could significantly ameliorate the menstrual pain compared with that before treatment and also resulted in high occurrence of menstrual-lilke bleeding during the drug withdrawal period with less number of days of irregular bleeding. However, the efficacy of a cyclic regimen of dienogest has not yet been studied for treatment of adenomyosis. Many of the pathophysiology of adenomyosis and endometriosis is quite similar. Both are originated from eutopic endometrium having somatic mutation and migrating to different sites e.g. peritoneal surface, ovary or myometrium. Therefore, this study aims to evaluate the efficacy of a cyclic regimen of dienogest for treatment of adenomyosis.