Daily hormonal birth control and emergency contraception (EC), such as Plan B, are two distinct methods of preventing pregnancy. Both daily oral contraceptives (OCPs) and dedicated emergency contraceptive pills (ECPs) use hormones, but they differ significantly in dosage, mechanism, and purpose. OCPs offer continuous, low-dose prevention, while ECPs provide acute, high-dose intervention. Understanding these differences is important for making informed decisions about contraception. This article provides educational information and is not a substitute for medical advice from a healthcare professional.
Standard Mechanism of Daily Contraceptives
Daily hormonal birth control pills are designed for long-term, consistent pregnancy prevention. Their mechanism relies on maintaining steady, low levels of synthetic hormones, typically a combination of estrogen and progestin, or progestin-only. Introducing these hormones suppresses the release of hormones that trigger ovulation, which is the primary way they prevent pregnancy.
The synthetic hormones also create secondary barriers. The progestin component causes the cervical mucus to become thicker and stickier, making it difficult for sperm to pass through the cervix and reach the egg.
A third mechanism involves the uterine lining, or endometrium, which becomes thinner. If an egg were fertilized, this thinner lining would be less receptive to implantation. These continuous, low-dose effects work best when the pill is taken consistently at the same time each day.
Emergency Contraception: A High-Dose Intervention
Emergency contraception (EC) is a reactive measure taken after unprotected intercourse or contraceptive failure. Dedicated oral ECPs use a single, much higher dose of hormones or a hormone blocker compared to a daily pill. The two main types of dedicated oral ECPs are those containing high-dose levonorgestrel (Plan B) and ulipristal acetate (Ella).
Levonorgestrel (Plan B)
This type works primarily by delaying or inhibiting ovulation. It is most effective when taken as soon as possible, ideally within 72 hours (three days) of unprotected sex. Effectiveness decreases significantly over time.
Ulipristal Acetate (Ella)
Ulipristal acetate (Ella), a selective progesterone receptor modulator, is effective for a longer window, up to 120 hours (five days) after unprotected sex. It can delay or inhibit ovulation, making it more effective than levonorgestrel later in the five-day window. Neither ECP is intended to terminate an established pregnancy; they prevent the pregnancy from starting.
Can Daily Pills Be Used for Emergency Protection?
It is possible to use certain combined oral contraceptive pills (OCPs) as emergency contraception, but this method is generally discouraged in favor of dedicated ECPs. This approach, called the Yuzpe method, requires taking a specific number of OCP tablets in two doses, 12 hours apart. The tablets must contain the correct amount of estrogen and levonorgestrel to reach the necessary high dose for emergency use.
Calculating the correct number of pills based on the specific hormone content of a patient’s daily pack makes this method complex and prone to error. The Yuzpe method is also less effective than modern dedicated ECPs, with an estimated effectiveness of about 74% compared to higher rates for levonorgestrel and ulipristal acetate.
Furthermore, the high dose of estrogen involved is associated with much more severe side effects, particularly nausea and vomiting, compared to a single-dose levonorgestrel pill. If vomiting occurs within two hours of taking a dose, the entire dose must be repeated, complicating the process further. Using daily pills for emergency protection is typically recommended only when dedicated emergency contraception is unavailable due to reduced effectiveness and increased side effects.