Comparative Study of 0.5 mg Dienogest Tablets (1 mg/Day) and Continuous Low-Dose Estrogen/Progestin for Dysmenorrhea: A Retrospective Analysis—Influence of Bleeding-Related Factors Such as Endometrial Polyps, Uterine Fibroids, and Adenomyosis

Background/Objectives: Dienogest 0.5 mg tablets (DNG0.5) taken twice daily (1 mg/day) are more effective than cyclic low-dose estrogen/progestin/combined oral contraceptive (LEP/COC) in ameliorating dysmenorrhea pain and are recommended for dysmenorrhea treatment in Japan. However, their efficacy has not been directly compared with continuous LEP/COC regimens. Here, we evaluated the effectiveness of DNG0.5 compared to Yazflex® (YZF), a continuous LEP, in treating dysmenorrhea. Methods: The efficacy of DNG0.5 in treating dysmenorrhea was compared retrospectively with that of Yazflex, the longest continuously administered LEP/COC available in Japan. Results: The improvement rates of dysmenorrhea scores at 3 and 6 months post-treatment were 59.1% and 66.4% in the LEP group (n = 113) and 88.1% and 96.4% in the DNG0.5 group (n = 125), respectively. The complete resolution rate of dysmenorrhea at 6 months was 88.0% in the DNG0.5 group and 23.9% in the LEP group. These findings indicate that DNG0.5 was significantly more effective than LEP (p < 0.01). DNG0.5 exerted an early pain-suppressing effect, which continued to increase thereafter. Furthermore, the presence of endometrial polyps, uterine fibroids, or adenomyosis, which are risk factors for irregular genital bleeding, was examined. Among these, endometrial polyps were particularly more likely to cause bleeding and potentially reduce the effect of DNG0.5; however, even with these three risk factors, DNG0.5 was more effective than LEP in reducing pain. Conclusions: Dienogest was more effective than LEP in managing dysmenorrhea, even at a dosage of 0.5 mg twice daily. However, factors affecting irregular vaginal bleeding should be considered when prescribing DNG0.5.