Combination oral contraceptives (COCs) are a widely used form of birth control that rely on a precise daily schedule to prevent pregnancy. Manufacturers package these medications in blister packs and use color coding to help users distinguish between different pills. This coloring signals a change in a pill’s function or hormonal content. The presence of pills in a distinct color, such as green, can cause confusion for users who are unsure if they are still receiving protection. Understanding the role of these differently colored pills is important for correctly using the medication and maintaining its effectiveness.
Identifying the Inactive Pills: Why They Are Green
The green pills found in many 28-day combination birth control packs are the inactive or placebo pills. These pills do not contain the synthetic hormones (estrogen and progestin) responsible for preventing conception. The green color provides a clear, visual cue that the active phase of the cycle has ended, and the hormone-free interval has begun.
Their inclusion serves a practical purpose: to help the user maintain the habit of taking a pill every single day. Taking an inert pill daily prevents the user from accidentally breaking the routine and forgetting to start the next pack of active pills on time. These placebo pills are sometimes referred to as “reminder pills.”
The composition of these inactive pills is generally inert, often consisting of sugar or starch. Some manufacturers may incorporate supplemental ingredients, such as a small dose of iron or folic acid, intended to address potential nutrient loss during the withdrawal bleed. These supplemental ingredients do not contribute to the pill’s contraceptive effect. The consistent daily intake of a pill, regardless of its content, ensures the user is prepared to begin the next pack of hormone-containing pills without a delay that could compromise protection.
How Hormones Prevent Pregnancy (The Active Phase)
The contraceptive action comes entirely from the non-green, active pills, which contain synthetic estrogen and progestin. These active pills are typically taken for 21 to 24 consecutive days before the placebo phase begins. The synthetic hormones suppress the body’s natural reproductive processes through a multi-layered mechanism.
The most significant action is the suppression of ovulation, preventing the release of an egg from the ovary. The synthetic hormones provide negative feedback to the pituitary gland, inhibiting the release of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). This prevents follicle development and stops the LH surge required to trigger ovulation.
The hormones also create a hostile environment for sperm. The progestin component thickens the cervical mucus, forming a physical barrier that makes it difficult for sperm to travel into the uterus. Additionally, the hormones cause the endometrium (uterine lining) to thin. While this thinning is a secondary mechanism, the primary protection comes from preventing ovulation and blocking sperm.
Navigating the Placebo Week
The week dedicated to taking the green inactive pills is known as the hormone-free interval or the placebo week. During this time, the sudden drop in hormone levels causes the uterine lining to shed, resulting in a withdrawal bleed. This bleed mimics a menstrual period but is a predictable response to the absence of synthetic hormones.
Contraceptive protection is maintained during this week, provided the preceding active pills were taken correctly and on schedule. The hormonal suppression remains effective because the brief pause in hormones is not long enough for the ovaries to resume ovulation.
Some users choose to skip the green pills and immediately begin a new pack of active pills, a practice known as cycle skipping. This is a safe method for intentionally delaying or eliminating the monthly withdrawal bleed. Not all hormonal contraception includes a placebo week; for example, many progestin-only pills contain 28 active pills with no hormone-free days.
For combination pill users, the green reminder pills ensure the cycle remains 28 days. Whether a user takes the green pills or skips them, the important action is starting the new pack of active pills no later than the eighth day after the last active pill was taken.