Plan B, also known as levonorgestrel, is an emergency contraceptive pill designed to prevent pregnancy. It serves as a backup method after unprotected sexual intercourse or when another form of contraception has failed. This medication intervenes before a pregnancy is established.
Understanding Plan B’s Mechanism
Plan B primarily works by preventing or delaying ovulation, the release of an egg. If an egg is not released, there is nothing for sperm to fertilize, thereby preventing pregnancy. The medication contains a higher dose of levonorgestrel, a synthetic hormone also found in some regular birth control pills.
Plan B does not directly affect fertilization or implantation, meaning it will not terminate an existing pregnancy. The drug acts by influencing the hormonal cycle to inhibit the processes necessary for conception.
Critical Timeframes for Effectiveness
Plan B is most effective when taken as soon as possible after unprotected sexual intercourse. The optimal window for taking it is within 72 hours (three days) of the event. Its effectiveness decreases as more time passes.
Studies suggest that when taken within 24 hours, it can be up to 95% effective. This efficacy drops to about 58% when taken between 48 and 72 hours after unprotected sex. While it can be used up to 120 hours (five days) post-intercourse, its effectiveness is significantly reduced after 72 hours. If ovulation has already occurred, Plan B cannot prevent pregnancy.
Factors Influencing Plan B’s Efficacy
Several factors can influence Plan B’s efficacy. Body weight is one consideration; the medication may be less effective for individuals above a certain body mass index (BMI). Some research suggests reduced efficacy for those weighing over 165 pounds or with a BMI greater than 25 kg/m2. Despite this, Plan B can still offer some effectiveness regardless of weight.
Certain medications can also reduce Plan B’s effectiveness. These include anti-seizure drugs like carbamazepine, phenytoin, and topiramate. Herbal supplements like St. John’s Wort, and drugs such as rifampin, bosentan, and felbamate, can interfere with its action. Consult a healthcare provider or pharmacist about current medications to understand potential interactions.
What Plan B Is Not
Plan B is not an abortion pill. Medication abortion uses a combination of medications to end an existing pregnancy. Plan B prevents pregnancy by inhibiting or delaying ovulation.
This medication is not intended for routine birth control. It contains a higher dose of hormones than daily birth control pills, making it unsuitable for regular use. Repeated use can lead to irregular menstrual cycles and is less effective than consistent, long-term birth control methods. Plan B also does not protect against sexually transmitted infections (STIs).
When to Seek Medical Guidance
After using Plan B, seek medical advice in specific situations:
- If a menstrual period is delayed by more than a week, take a pregnancy test and consult a healthcare provider. This delay could mean the emergency contraception was unsuccessful.
- Severe abdominal pain three to five weeks after taking Plan B warrants immediate medical attention, as it could signal an ectopic pregnancy. An ectopic pregnancy occurs when a fertilized egg implants outside the uterus and can be life-threatening.
- If vomiting occurs within two hours of taking Plan B, another dose might be necessary; contact a healthcare professional.
- Discuss regular contraception options with a healthcare provider for ongoing pregnancy prevention and STI concerns.