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Effect Of Body Weight or BMI On Effectiveness Of Emergency Contraceptive Pill

Understanding the nuances of how body weight or Body Mass Index (BMI) can impact the effectiveness of an emergency contraceptive pill (ECP) is essential. This blog delves into the scientific underpinnings of this correlation.

Science Behind An Emergency Contraceptive Pill

Emergency contraceptive pill (ECP) is a critical tool in preventing unintended pregnancies following unprotected sex (when no contraception is used) or contraceptive failure (for example, when the condom breaks, slips, or leaks during sex).

This pill works primarily by delaying ovulation, ensuring that sperm cannot meet an ovum for fertilization. However, the effectiveness of this contraceptive method can vary based on several factors, including the user's body weight or BMI.

how does an emergency contraceptive pill or ecp or morning after pill or plan b or ipill or unwanted pill work

Body Weight And Effectiveness Of An Emergency Contraceptive Pill

Recent studies indicate that higher body weight or BMI can reduce the effectiveness of an ECP. Which means that individuals with higher BMIs and weights can experience a higher risk of ECP failure.

The primary hypothesis is that the distribution and metabolism of the drug in larger body masses may decrease its concentration in the bloodstream, reducing its efficacy.

Regardless, the studies concluded that an ECP should be taken, irrespective of body weight or BMI, as soon as possible after unprotected sex.

effect of body weight or bmi on effectiveness of emergency contraceptive pill or ecp or morning after pill or plan b or ipill or unwanted pill

Possible Solutions And Alternatives

For individuals with a higher BMI, the following approaches are recommended:

  • Timing is Key: Taking the pill as soon as possible after unprotected sex can help maximize its potential effectiveness.

  • Alternative Methods: Consulting a doctor to discuss other forms of emergency contraception, such as the copper IUD (intrauterine device), which has been shown to be effective regardless of BMI, when used up to 5 days after unprotected sex.


The intersection of body weight and efficacy of an emergency contraceptive pill (ECP) is a testament to the complexity of human biology and pharmacology. By acknowledging and addressing these variations, individuals can make informed decisions about their contraceptive use. Always consult a doctor to tailor the advice to your specific health profile and needs.


This blog, including its text, images, and infographics, are for educational purposes only and not a substitute for professional medical advice. For personalized advice, always consult a doctor.

Further Reading

For more details on this or related topics, refer to the papers listed in references below, the FAQs on the ECP page, or other blogs on the Learn page of our website


  • Contraception. Effect of body weight and BMI on the efficacy of levonorgestrel emergency contraception. 2015.

  • Contraception. Effect of BMI and body weight on pregnancy rates with LNG as emergency contraception: analysis of four WHO HRP studies. 2017.

  • Current Medical Research and Opinion (CMRO). Levonorgestrel emergency contraception and bodyweight. 2019.


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