Eb2017 asked
I weigh 350 pounds and I just took Plan B. Will it be effective?
Answer
One large analysis of various studies showed that across all weight groups, pregnancy rates with the use of Plan B (levonorgestrel) were low, at less than 3%. However, there was a considerable increase in pregnancy rates in women considered obese according to the BMI (Body mass Index) scale (BMI >30kg/m2).
Another analysis that included over 1700 women found similar results. According to the data, the group of women studied that weighed between 65-75 kg (143-165 pounds) had a pregnancy rate of 1.4%. The group of women that weighed over 85 kg (187 pounds) had a pregnancy rate of 5.7%.
One of the largest studies on this matter was completed in 2017 and included over 6500 women. The overall pregnancy rate in all groups was 1.2%. The rate was slightly higher at 2.0% for those considered obese. Like the other studies mentioned, the efficacy of the emergency contraception decreased when compared to women who had a lower BMI, although not as significantly as some other studies found.
Nevertheless, it is important to emphasize that emergency contraception IS effective in all weight groups, just slightly less so in obese individuals. Both the World Health Organization (WHO) and the Food & Drug Administration (FDA) state that all women, regardless of weight, can use emergency contraception products to prevent unintended pregnancy and there is no listed warning in regard to weight. In addition, the most important factor in regard to how well emergency contraception works is how soon after unprotected sex it is taken.
In regard to why weight may be a influencing factor on the efficacy of emergency contraception, there are a few theories.
First, a higher body weight is associated with a higher basal metabolic rate, leading to a shorter duration of action of emergency contraceptives.
Second, hormones may have increased clearance rates in obese individuals due to increased hepatic metabolism. This could lead to lower than usual drug levels in the body.
Lastly, many hormones are lipophilic and may be stored inside fat tissue. The more fat tissue there is, the lower the hormone levels in the blood which could lead to lower overall efficacy.
If you have questions or concerns about the efficacy of Plan B in your situation, please reach out to your doctor.
