Medically reviewed by Alan Lucks | MD, Alan Lucks MDPC Private Practice - New York on February 6th, 2026.
Plan B prevents up to 89% of potential pregnancies when taken within 72 hours
Effectiveness decreases significantly after 24-48 hours
Body weight and timing can impact emergency contraception performance
Follow-up with regular birth control is recommended
Emergency contraception represents an important reproductive health option for individuals seeking to prevent unintended pregnancy. Plan B One-Step offers a critical backup method when primary contraception fails or is unavailable. Understanding its mechanisms, effectiveness, and potential limitations can help individuals make informed healthcare decisions.
Plan B contains levonorgestrel, a synthetic hormone that primarily prevents pregnancy by stopping or delaying ovulation. When taken before an egg is released, the medication can effectively block fertilization. It works by altering the reproductive environment, making birth control more strategic and responsive.
The hormone is quickly absorbed, reaching peak blood levels within two hours of ingestion. Importantly, Plan B is not an abortion medication but a preventive measure that intervenes before pregnancy can be established.
Plan B's effectiveness is dramatically time-sensitive. Here's a breakdown of prevention rates:
Timing After Intercourse |
Pregnancy Prevention Rate |
|---|---|
First 24 hours |
95% |
24-48 hours |
85% |
48-72 hours |
58% |
72-120 hours |
Approximately 50% |
Multiple variables can impact Plan B's performance. Body weight is a significant consideration, with reduced effectiveness potentially occurring in individuals over 165 pounds. Healthcare providers recommend consulting a medical professional for personalized guidance.
Certain medications can also interfere with Plan B, including:
Anticonvulsants
Rifampin antibiotics
St. John's Wort supplements
Most individuals experience temporary side effects such as:
Menstrual cycle changes
Nausea
Fatigue
Headache
Abdominal discomfort
Vomiting
Dizziness
Fatigue
Breast tenderness
No emergency contraception is 100% guaranteed. Plan B prevents approximately 89% of potential pregnancies.
The sooner, the better. Effectiveness is highest within the first 24 hours after unprotected intercourse.
No, it's designed for emergency use only. Regular birth control methods are more reliable and consistent.
Yes, individuals over 165 pounds may experience reduced effectiveness.
Consult a healthcare provider. Vomiting within two hours might require another dose.
Emergency contraception provides an important reproductive health option, but it's not a substitute for regular birth control. Care you can trust. Doctronic is clinically validated with 99% treatment plan alignment.
Emergency contraception represents an important reproductive health option for individuals seeking to prevent unintended pregnancy. Plan B One-Step offers a critical backup [...]
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