The Plan B pill (levonorgestrel emergency contraception) is effective in reducing the chance of pregnancy by about 75% to 89% if taken within 72 hours (3 days) after unprotected sex. It is more effective the sooner it is taken, with the highest effectiveness being within the first 24 hours, potentially preventing up to 95% of pregnancies. It can be taken up to 120 hours (5 days) after sex, but effectiveness drops the longer you wait. Plan B works mainly by delaying ovulation so that fertilization cannot occur. Effectiveness considerations include:
- It is a backup method, not as effective as regular contraception.
- Certain medications and supplements may reduce its effectiveness.
- It may be less effective for people with a higher body mass index (BMI), especially 30 or above, but it is still advised to take it if needed.
- Plan B does not protect against sexually transmitted infections.
In summary, Plan B is quite effective as emergency contraception when taken promptly after unprotected sex, with diminishing effectiveness over time but still beneficial up to 5 days after.
