Combined oral contraceptives (COCs) are typically packaged in a 28-day format, including two types of pills: “active” and “inactive.” Active pills contain synthetic estrogen and progestin, which regulate the cycle and prevent pregnancy. The inactive pills are often distinguished by color, such as white. This packaging structure helps users maintain a daily routine for maximum effectiveness.
What are the Inactive Pills?
The “white pills” are the inactive pills, also known as placebo or reminder pills. These pills do not contain any of the hormones (estrogen or progestin) found in the active pills. The primary purpose of including these hormone-free pills is to help the user maintain the routine of taking a pill at the same time every day. In some brands, these inactive pills may contain supplements like iron, but they still lack the contraceptive hormones.
The Role of Hormonal Withdrawal
The active pills contain hormones that stabilize hormone levels and prevent the uterine lining from thickening significantly. These synthetic hormones mimic natural hormones, preventing the body from preparing for a potential pregnancy. When a person stops taking the active pills and begins the inactive pills, the sustained level of circulating hormones drops sharply. This sudden drop in estrogen and progestin levels is the physiological trigger for the bleeding to begin. Therefore, the absence of active hormones initiates the shedding of the uterine lining, not any ingredients within the inactive pills themselves.
The active pills are usually taken for 21 to 24 days, followed by a shorter period of inactive pills. This hormone-free interval causes the stabilized lining of the uterus to break down and shed, resulting in bleeding. The bleeding typically starts two to four days after the last active pill is taken, coinciding with the first few days of taking the inactive pills.
Withdrawal Bleeding Versus a True Period
The bleeding that occurs during the inactive pill week is scientifically termed “withdrawal bleeding,” which is distinct from a true menstrual period. A true menstrual period follows the natural cycle of ovulation, where an egg is released and the uterine lining thickens. Since combined oral contraceptives prevent ovulation from occurring, the monthly bleeding is not considered a true period.
Withdrawal bleeding is often lighter and shorter in duration than a typical menstrual period because the hormones in the pill prevent the uterine lining from fully developing. For some people, the bleeding can be very light or may not occur at all, which is a normal variation, especially with continuous-dose pills. If withdrawal bleeding does not occur, and the user has been taking the active pills consistently, it may not be a cause for concern, but a pregnancy test is often recommended if pills were missed.