Medically reviewed by Alan Lucks | MD, Alan Lucks MDPC Private Practice - New York on February 7th, 2026.
Plan B prevents pregnancy but is not 100% guaranteed
Effectiveness depends on timing, body weight, and ovulation cycle
Most effective when taken within 72 hours of unprotected sex
Consulting a healthcare provider can help you understand your options
Emergency contraception provides an important safety net for individuals seeking to prevent unintended pregnancy. While Plan B is a widely used option, understanding its limitations and effectiveness is crucial for making informed reproductive health decisions.
Plan B contains levonorgestrel, a synthetic hormone that primarily prevents pregnancy by delaying or stopping ovulation. When taken promptly after unprotected sexual intercourse, it can significantly reduce pregnancy risk. However, its effectiveness is not absolute and depends on multiple physiological factors.
The success rate of Plan B varies based on several critical elements. Understanding the risks of birth control helps individuals make more informed choices about emergency contraception.
The most crucial factor in Plan B's effectiveness is how quickly it's taken after unprotected sex. The medication works best when consumed within 24 hours, with efficacy gradually decreasing over 72 hours. After this window, the likelihood of preventing pregnancy significantly reduces.
Research indicates that birth control effectiveness can be influenced by body weight. Women with a body mass index (BMI) over 30 or weighing more than 175 pounds might experience reduced Plan B efficacy.
If ovulation has already occurred when Plan B is taken, the medication cannot prevent potential fertilization. This means the emergency contraceptive's window of effectiveness is relatively narrow.
Most individuals experience mild side effects such as:
Slight menstrual irregularities
Minor abdominal cramping
Temporary hormone fluctuations
Potential changes in next menstrual cycle
Nausea and vomiting
Fatigue
Dizziness
Headache
Breast tenderness
Side Effect |
Duration |
Typical Management |
|---|---|---|
Cramping |
1-2 days |
Over-the-counter pain relievers |
Irregular bleeding |
1 menstrual cycle |
Rest and hydration |
Nausea |
24-48 hours |
Small, frequent meals |
Fatigue |
1-2 days |
Extra rest |
If you experience severe symptoms or your period is more than a week late, medical gaslighting should not prevent you from seeking help. Consult a healthcare professional for personalized guidance.
Q: Can Plan B be used multiple times? A: While possible, it's not recommended as a regular contraception method. Repeated use can disrupt hormone balance.
Q: How soon after taking Plan B should I worry about pregnancy? A: Take a pregnancy test if your period is more than a week late.
Q: Are there alternatives to Plan B? A: Consult a healthcare provider about various emergency contraception options.
Q: Does alcohol impact Plan B's effectiveness? A: Moderate alcohol consumption does not significantly reduce the medication's efficacy.
Q: Can Plan B protect against sexually transmitted infections? A: No. Plan B only prevents pregnancy and does not protect against STIs.
Emergency contraception provides an important reproductive health option, but it's not infallible. Individual factors significantly impact its effectiveness. Ready to get personalized guidance? Skip the waiting room. Get answers in minutes with Doctronic.
Emergency contraception provides an important safety net for individuals seeking to prevent unintended pregnancy. While Plan B is a widely used option, understanding its [...]
Read More
