Abstract

Combined oral contraceptives (COCs) are highly effective when correctly used but unscheduled bleeding, which occurs fairly commonly during the early months, is disruptive for many women. The mechanisms underlying this bleeding are not fully understood. Several studies have shown that extended-cycle or continuous-use COCs are typically associated with higher initial rates of unscheduled bleeding than are conventional 21-day cyclical COCs. Some medicines, herbal supplements and smoking may increase unscheduled bleeding by interfering with estrogen metabolism. The most common cause of unscheduled bleeding is non-adherence to a prescribed COC regimen. Compliance can be improved by appropriate counselling of women about the possibility of unscheduled bleeding and the importance of adherence to the pill regimen. If abnormal bleeding persists beyond 3–4 months and causes such as incorrect usage can be ruled out, other causes should be considered.