Effectiveness, safety and acceptability of continuous or extended-cycle use of combined oral contraceptives (COCs): a systematic review and meta-analysis.

BACKGROUND: To evaluate the contraceptive effectiveness, safety and acceptability of continuous or extended-cycle combined oral contraceptives (COCs) compared with conventional cyclic regimens (21/7 or 24/4). METHODS: A systematic search was conducted in Medline, Embase, Web of Science, trials registries and other databases from 1 January 1970 to 21 October 2024. Complementary searches were conducted in grey literature sources and reference lists. RESULTS: A total of 9531 records were identified, from which 18 randomised controlled trials and 10 studies of other designs were included. Overall, findings indicated that: (1) continuous or extended-cycle COCs had contraceptive effectiveness similar to cyclic COCs (unintended pregnancies over 1 year: OR 0.79, 95% CI 0.41 to 1.52; Pearl Index mean difference -0.20, 95% CI -1.31 to 0.92); (2) bleeding outcomes varied, with either no significant difference or fewer total bleeding and/or spotting days with continuous or extended-cycle COC use, but more unscheduled bleeding; (3) no significant difference was observed in the odds of experiencing at least one adverse event (OR 1.20, 95% CI 1.03 to 1.41); (4) the relative risk of deep vein thrombosis or venous thromboembolism was low (OR 1.05, 95% CI 0.16 to 6.79), with a small absolute increase (approximately 0.7 additional cases per 1000 users); and (5) satisfaction was generally high in both groups. CONCLUSIONS: Continuous or extended-cycle COC use demonstrates comparable contraceptive effectiveness, safety and overall acceptability to conventional cyclic COC regimens. However, interpretation of acceptability and bleeding-related outcomes should consider higher discontinuation rates and missing outcome data.