What's the weight limit for Plan B?

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Official answer

by Drugs.com

Despite what many people believe, there is no official weight limit for Plan B One-Step and there is no weight recommendation on the FDA label for Plan B. There is currently no reason or good evidence that women of a higher body weight or BMI cannot use Plan B or other forms of emergency contraception (EC).

This belief that weight affects EC effectiveness stems from a 2011 meta-analysis that concluded women with a BMI >30 kg/m2 had at least a three-fold higher rate of pregnancy. A subsequent investigation by the European Medicines Agency and a Cochrane review did not find an association between higher BMI or weight and lower effectiveness of hormonal contraceptives, although there were few studies and the evidence quality was variable. Most studies that were reviewed did not show a higher pregnancy risk among overweight or obese women with emergency contraception (EC), such as Plan B.

Why do some sources say not to use Plan B or other emergency contraceptives in women over 165 pounds (75kg)?

This recommendation stems from a meta-analysis by Glasier et al, published in 2011 in the journal, Contraception, that looked at pregnancy rates from 2 randomized controlled trials comparing levonorgestrel-based ECs (such as Plan B) to ulipristal acetate (UPA, Ella). This meta-analysis found:

  • A three times higher rate of pregnancy for women with a BMI >30 kg/m2 than those with a normal BMI (<25 kg/m2), regardless of which EC was used
  • Levonorgestrel-based EC was associated with a greater risk of pregnancy OR, 4.41; 95% CI, 2.05Y9.44; P = 0.0002) than with the use of UPA (OR, 2.62; 95% CI, 0.89Y7.00; NS)
  • Women were more likely to get pregnant if unprotected sexual intercourse occurred the day before the estimated date of ovulation (four-fold risk; OR, 4.42; 95% CI, 2.33Y8.20; P = 0.0001) compared to those having sex outside the fertile window
  • Women who had unprotected sexual intercourse in the days following EC use were also more likely to become pregnant (OR, 4.64; 95% CI, 2.22Y8.96; P = 0.0002).
  • The authors concluded that women who have intercourse around the time of ovulation should use a copper IUD and that UPA or the IUD is more effective in overweight or obese women.

    • This meta-analysis had a huge impact on EC prescribing worldwide, with many women being refused emergency contraception if they looked over 165 pounds (75kg). Considering the average woman in the U.S. weighs 166.2 pounds, this represented a lot of women.

    In 2014, the European Medicines Agency commission a review and concluded:

  • The data available do not support with certainty the conclusion that contraceptive effectiveness is reduced in women with high body weight
  • Emergency contraceptives should be taken as soon as possible after unprotected intercourse
  • Remind women that emergency contraception is an occasional “rescue” method and does not work as well as regular methods of contraception
  • Emergency contraceptives should continue to be used if the benefits outweigh the risks.

    • A Cochrane review (Lopez et al, 2016) of 17 studies (63,813 women) concluded the evidence did not support an association between higher BMI or weight and hormonal contraceptive effectiveness but the overall quality of evidence was low.

    Another study conducted on 10 women (5 with a normal BMI and 5 with a BMI >35 kg/m2) found that levels of levonorgestrel EC were significantly lower in women with a higher BMI than those with a normal BMI. Taking a double dose of the levonorgestrel EC increased blood concentrations significantly, and were comparable to those in women with normal BMI. Although doubling the dose of EC appears an effective strategy to increase blood levels of levonorgestrel, it is currently not known what effect a double dose of EC has on pregnancy rates or the likely increase in side effects in addition to increased cost. A double-dose is not listed as an option of the Plan B Product label.

    What should I do if I have unprotected sex and I weigh more than 165 pounds (75kg)?

    Although most sources agree a copper IUD is the most effective emergency contraceptive option for women of all bodyweights, trying to get a same-day appointment in addition to the side effects of having an IUD placed (such as cramping), plus the cost, makes this option not viable for many women.

    Although body weight may or may not be a factor in the failure rate of emergency contraception, it is just one of several factors that can have an impact. If you have unprotected sex and you do not want to become pregnant but cannot afford or want to get a copper IUD inserted then lower your risk of pregnancy by doing all of the following:

  • Take the emergency contraceptive pill (Plan B or Ella) as soon as you can. If you are due to ovulate, take it right now! It is more effective the earlier you take it and if you are close to ovulating then you have a higher chance of getting pregnant, even if you take it, no matter what your weight is. It must be taken within 72 hours (levonorgestrel ECs such as Plan B), or 120 hours for UPA (Ella), but if you wait till the end of the effectiveness window, you may still become pregnant
  • Do not have any additional unprotected intercourse until you get your period or until a regular form of birth control has had enough time to start working
  • Start a regular form of contraception the day you take the EC.

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