REMINDER: if you have a vagina and want to use Plan B as an emergency contraceptive, it loses effectiveness if you weigh more than 165 lbs (74.84 kg) and is completely ineffective for those that weight more than 176 lbs (79.83 kg) (x)
This is horrifying. And sadly true.
The idea of efficacy being affected by BMI has really recently been called into question, I’ve actually been writing up some stuff about this for my job, here’s a little more information about this:
- "Having assessed all the available evidence on the effectiveness of emergency contraceptives, the CHMP considered that the data available are too limited and not robust enough to conclude with certainty that contraceptive effect is reduced with increased body weight, as stated in the product information for Norlevo,” the EMA said.” - "Weight Not a Factor in Emergency Contraception: EMA Panel," Megan Brooks, Medscape
- Here’s the press release regarding the start of the literature review by the European Medicines Agency.
- Here’s a press release regarding the same study quoted above, also by the European Medicines Agency.
- Here’s another overall review of existing literature from the Cochrane Collaboration, “We found 9 reports with data from 13 trials and 49,712 women. Five reports from 2002 to 2012 compared BMI groups. Only one found more pregnancies among overweight or obese women using one of the combined birth control pills.”
I don’t quite have time to track down any literature specifically about Plan B, but overall it’s better to take whatever form of emergency contraception is appropriate, healthy and available (if necessary) than to not. It looks like by far the most important factor in emergency contraception is to not delay taking it, so it’s recommended that anyone who is in need of EC take it as soon as possible regardless of BMI or weight.