Factors influencing continuation of combined oral contraceptives in women with dysmenorrhea or endometriosis: A retrospective cohort study utilizing a claims database in Japan

Purpose: To identify factors influencing continuation of combined oral contraceptives (COCs) in women with dysmenorrhea or endometriosis. Methods: This retrospective cohort study included women initiated on low-dose (LD) or ultra-low-dose (ULD) COCs from 2005-2021 in Japan. We used Kaplan–Meier analysis to estimate COC continuation probabilities based on factors like COC generation, ethinylestradiol content, and prescription years. We also calculated the proportion of patients who switched to the COC generation before discontinuation. Results: We identified 73,146 women with an initial COC prescription. First-generation COCs accounted for 40,167 women (54.9%) of the initially prescribed COCs. First-generation LD was prescribed more frequently in earlier years, with 22.7% of cases prescribed before 2017, compared with first-generation ULD (10.6%), second-generation (0%), and fourth-generation (11.2%). The continuation probability (95% confidence interval [CIs]) after 180 days was slightly lower in those who initiated first-generation LD (0.49 [0.48, 0.50]) compared with first-generation ULD (0.52 [0.51, 0.53]), second-generation (0.54 [0.52, 0.56]), and fourth-generation (0.50 [0.49, 0.50]) COCs. The continuation probability improved over time from 0.43 [0.42, 0.44] before 2017 to 0.57 [0.56, 0.58] in 2021. Women who switched to other COCs accounted for 3.5–8.7% of patients while 36.8–44.3% of patients discontinued COCs without switching. Approximately three-quarters of women who switched to another COC continued using COCs. Conclusion: COC adherence among Japanese women with dysmenorrhea or endometriosis improved over the years while the apparent differences in COC categories prescribed may reflect this trend. Encouraging patients to switch to different COC generations may further enhance adherence to COCs.