Understanding Emergency Contraception
Plan B One-Step, often called the “morning-after pill,” is a form of emergency contraception (EC) used to prevent pregnancy after unprotected intercourse or a known contraceptive failure [1.7.5]. It contains a high dose of levonorgestrel, a synthetic hormone called progestin that is also found in many regular birth control pills [1.5.2, 1.9.2]. It is important to note that Plan B is intended as a backup method and is not as effective as regular contraceptive methods for ongoing pregnancy prevention [1.7.5]. It also does not protect against sexually transmitted infections (STIs) [1.3.3].
What Does Plan B Do Exactly? The Primary Mechanism
The primary and most understood way Plan B works is by preventing or delaying ovulation [1.2.2, 1.2.4]. Ovulation is the process where an ovary releases an egg. For pregnancy to occur, sperm must meet and fertilize this egg. By taking Plan B, the surge of hormones temporarily stops the ovary from releasing an egg. If there's no egg for sperm to meet, fertilization cannot happen, and pregnancy is prevented [1.2.2]. The timing is critical; Plan B is most effective when taken before ovulation has occurred [1.3.5]. It is not effective if you have already ovulated [1.3.4].
Some older product labels suggested that Plan B might also work by preventing a fertilized egg from implanting in the uterus [1.2.5]. However, the scientific consensus and updated information from the FDA indicate that the principal effect is the delay of ovulation [1.2.1, 1.7.4]. Plan B is not an abortion pill; it does not interrupt an established pregnancy [1.6.2, 1.7.2]. If you are already pregnant, Plan B will not work and will not harm the existing pregnancy [1.7.4, 1.7.5].
Effectiveness: How Well Does It Work?
The effectiveness of Plan B depends heavily on how soon it is taken after unprotected sex. It should be taken within 72 hours (3 days) [1.3.3].
- Within 24 hours: It can be around 95% effective at preventing pregnancy [1.2.3, 1.3.2].
- Within 72 hours: The overall effectiveness is about 87-89% [1.3.3, 1.3.4].
Its effectiveness decreases the longer you wait [1.2.3]. Some studies suggest it may have some moderate effectiveness up to 120 hours (5 days) after intercourse, but it is significantly less effective by that point [1.10.2].
Certain factors can influence its efficacy. Research suggests that Plan B may be less effective for individuals with a Body Mass Index (BMI) over 25 or who weigh more than 165 pounds [1.3.4, 1.5.4]. However, it is still recommended to take it if needed, as it can still provide some protection [1.3.4].
Comparison of Emergency Contraceptives
Plan B is not the only option for emergency contraception. Another pill, ella®, and the copper IUD are also available.
| Feature | Plan B One-Step (Levonorgestrel) | ella® (Ulipristal Acetate) | Copper IUD |
|---|---|---|---|
| Active Ingredient | 1.5 mg Levonorgestrel [1.2.3] | 30 mg Ulipristal Acetate [1.5.5] | Copper [1.6.3] |
| Effective Window | Up to 72 hours (3 days) [1.10.4] | Up to 120 hours (5 days) [1.5.3] | Up to 120 hours (5 days) [1.6.3] |
| Effectiveness | 75-89% effective [1.10.4] | More effective than Plan B, especially closer to ovulation [1.3.1, 1.5.4] | Over 99% effective [1.3.1] |
| Availability | Over-the-counter, no prescription or ID needed [1.3.3, 1.9.3] | Prescription only [1.5.2, 1.5.5] | Must be inserted by a healthcare provider [1.3.1] |
| Weight Considerations | May be less effective if over 165 lbs [1.5.4] | May be less effective if over 195 lbs [1.5.2] | Works just as well regardless of weight [1.5.4] |
Potential Side Effects and Menstrual Changes
Like any medication, Plan B can cause side effects, though they are usually mild and temporary, lasting only a few days [1.4.1, 1.4.4].
Common Side Effects Include:
- Nausea or vomiting [1.4.2]
- Headache [1.4.2]
- Dizziness [1.4.2]
- Fatigue [1.4.2]
- Lower abdominal cramps [1.4.2]
- Breast tenderness [1.4.2]
Taking the pill can also affect your next menstrual period. Your period might come earlier or later than usual, and the flow could be heavier or lighter [1.8.2, 1.8.4]. Spotting or bleeding between periods is also common [1.8.2]. If your period is more than a week late after taking Plan B, you should take a pregnancy test [1.4.2].
Dispelling Common Myths
There are many misconceptions about emergency contraception. It's important to separate fact from fiction.
- Myth: Plan B is an abortion pill. Fact: Plan B prevents pregnancy primarily by stopping ovulation. It does not terminate an existing pregnancy [1.6.4, 1.7.2].
- Myth: You can only use Plan B a few times in your life. Fact: It is safe to take Plan B whenever needed, although it should not replace regular birth control due to lower effectiveness and potential for cycle disruption [1.6.2, 1.6.5].
- Myth: Taking Plan B will affect future fertility. Fact: Plan B does not impact your long-term fertility [1.6.1, 1.7.5].
Accessibility and Cost
Plan B One-Step and its generic versions are available over-the-counter (OTC) in the United States at most drugstores and pharmacies [1.9.3, 1.9.5]. There are no age or ID requirements to purchase it [1.9.3]. The cost typically ranges from $40 to $50, with generic versions sometimes being cheaper [1.9.2, 1.9.3]. It may also be available for free or at a lower cost through health clinics like Planned Parenthood, or covered by insurance with a prescription [1.9.1, 1.9.4].
Conclusion
To answer the question, 'What does Plan B do exactly?', it is an emergency contraceptive that works primarily by delaying or preventing the release of an egg from the ovary, thereby preventing fertilization. It is a safe and effective backup option to reduce the risk of pregnancy when taken within 72 hours of unprotected sex or contraceptive failure. It is not an abortion pill and has no effect on an existing pregnancy or future fertility. Understanding its mechanism, effectiveness, and proper use empowers individuals to make timely and informed choices for their reproductive health.
For more information, you can visit Planned Parenthood..
