Plan B is an emergency contraceptive designed for use after unprotected sexual intercourse or when a primary birth control method has failed. It offers a time-sensitive option to help prevent pregnancy. This medication is not intended for routine contraception but rather as a backup measure.
Plan B’s Primary Mechanism: Delaying Ovulation
Plan B contains the synthetic hormone levonorgestrel, which primarily works by affecting ovulation. Levonorgestrel mimics progesterone, influencing the luteinizing hormone (LH) surge that precedes egg release. By suppressing or delaying this LH surge, Plan B can prevent the ovary from releasing an egg. This mechanism ensures that if an egg is not released, there is nothing for sperm to fertilize, thereby preventing pregnancy. Its effectiveness is highest when taken before ovulation has occurred.
What Happens If Ovulation Has Already Occurred?
If ovulation has already occurred, Plan B’s main mechanism of delaying egg release is no longer effective. The medication does not terminate an existing pregnancy or affect a fertilized egg that has already implanted. Plan B is not an abortion pill; it prevents pregnancy from establishing, rather than ending one. Therefore, if an egg has been released and potentially fertilized, Plan B’s effectiveness is significantly reduced or entirely absent.
Key Factors for Plan B’s Effectiveness
Timing is a key factor influencing Plan B’s effectiveness. It is most effective when taken as soon as possible after unprotected sex. While it can be taken up to 72 hours (3 days) after intercourse, its ability to prevent pregnancy decreases with each passing hour. While some sources suggest effectiveness up to 5 days, earlier use is more effective.
Body weight can also influence Plan B’s effectiveness. Research indicates that levonorgestrel-based emergency contraception might be less effective in individuals weighing 155 pounds or more. For those weighing above approximately 165 pounds, alternative emergency contraception options like Ella (ulipristal acetate) or a copper IUD might be more suitable. Despite these considerations, taking Plan B is generally considered better than taking no emergency contraception at all, regardless of body weight.
Side Effects, What to Expect, and When to Consult a Doctor
After taking Plan B, individuals may experience several temporary side effects. Common reactions include nausea, fatigue, headaches, dizziness, breast tenderness, and lower abdominal cramps. Vomiting or diarrhea may also occur.
Changes to the menstrual cycle are typical. The next period might be early, late, heavier, or lighter than usual. Spotting or irregular bleeding before the next expected period can also occur. If the period is delayed by more than a week, or if there are concerns about pregnancy, taking a pregnancy test is advised.
Consult a healthcare professional if side effects are severe or persist for more than 48 hours. Seek immediate medical attention for severe lower abdominal pain, especially if it occurs three to five weeks after taking Plan B, as this could indicate an ectopic pregnancy. A healthcare provider can also discuss ongoing contraception options.