I have heard that Plan B doesn’t work if you are over a certain weight, like about 170 lb. For women over that, can you take 2 pills? Do you have any advice on that? I’m sure I’m not the only woman wondering about that.
Plan B, the emergency contraceptive or EC, is an effective method of contraception when used as directed, but the failure rate may be higher for those with a body mass index (BMI) > 30 or higher.
Plan B is a single 1.5 mg dose of the hormone levonorgestrel. When taken within five days of a single act of unprotected intercourse it reduces the risk of pregnancy by 61-95%. Most studies suggest it is most effective within 72 hours, and the sooner it is taken the better (which accounts for the range in effectiveness). A more practical way of looking at it is to ask what is the chance you could be pregnant if you took Plan B? The answer is approximately 1.2-2.6% depending on which studies you use.
Plan B works by stopping what is called the surge of luteinizing hormone or LH from the brain. High levels of LH help prepare the egg for ovulation and this surge is required for ovulation. No LH surge, no ovulation.
What we know about BMI/weight and Plan B is conflicting. Some studies have shown a reduced effectiveness based on increased BMI/weight, but others have not. Among studies that show a reduction in effectiveness, some show a dramatic reduction, while in others the impact is much less. Some research has shown the blood levels of the hormone levonorgestrel are about 50% lower for those who are obese, yet other data has shown that while they are lower, they are still high enough to prevent ovulation.
While reading the studies I found myself yelling, “Come on!”, in frustration.
There are two big issues with the clinical trials. First is that most of the studies looking at pregnancy rates have low numbers of participants with a body mass index of 30 or greater. The second is that none of the studies were designed to specifically address the impact of weight or BMI on effectiveness of Plan B. Basically, drawing hard conclusions from these studies isn’t possible. This is not acceptable, but unfortunately, that is the state of affairs.
Overall the data suggests that Plan B may be less effective for women with a BMI of 30 or greater, and this is something people should know. This is reflected in all of the expert consensus statements. There is currently a study underway that is looking at a double dose of Plan B for women with a BMI of 30 or greater, but we don’t have any results yet, so that doesn’t help right now.
What we know for sure:
The IUD (the copper or the 52 mg levonorgestrel) is the most effective form of emergency contraception and it is unrelated to weight. For anyone who absolutely does not want to be pregnant, regardless of weight or BMI, this is your best bet.
The other oral form of emergency contraception, ulipristal acetate or UPA, (trade name Ella), is slightly more effective than Plan B and appears to be less impacted by BMI/weight. If you do not want to be pregnant, regardless of weight or BMI, and a pill is what is right for you then this is your best bet. In the United States it is generally more expensive than Plan B and requires a prescription, while Plan B does not.
Here are some recommendations from several groups regarding BMI/weight and Plan B:
The World Health Organization
Their opinion is that emergency contraceptive pills are less effective for those with a body mass index more than 30, but that “obese women should not be denied access to emergency contraception when they need it”. A review of four studies referenced in the WHO guidelines found the pregnancy rate was 2.03% for women with a BMI of 30 or higher and 1.25% for those with a BMI of 25 or less.
American College of Obstetricians and Gynecologists
They state that body weight influences the effectiveness of oral emergency contraception and recommend that physicians advise their patients that an IUD is better, but to not withhold Plan B.
The International Consortium for Emergency Contraception
This group writes that “Plan B may be less effective among women with a body mass index (BMI) ≥30 kg/m2 than among women with a BMI <25 kg/m2. The copper IUD or the UPA regimen is recommended or a double dose of Plan B can be considered. Women should never be denied access to Plan B due to higher weights or BMI.”
Faculty of Sexual & Reproductive Healthcare (FSRH) (United Kingdom)
Advise that women should be informed that the copper IUD is the most effective method of emergency contraception and that BMI >25 or weight >70 kg may reduce the effectiveness or the oral options, particularly of Plan B. They also state that women with a BMI > 26 or who weigh > 70 kg should consider UPA and, if this is not suitable, they should double-dose (3 mg) LNG-EC, understanding the effectiveness of a double-dose LNG-EC is unknown.
If you have a BMI of 30 or more or weigh 70 kg or more (which is a lot of people), Plan B will reduce your risk of getting pregnant, but it may not be the most effective choice.
For those who want an oral option for emergency contraception, consider the following:
If all you have is the standard 1.5 mg dose of Plan B, use it. It is still effective. It just may not be as effective.
If UPA is an option, it is preferred as studies show less of an impact of BMI/weight.
Consider a double dose of Plan B, understanding that studies don’t tell us if this is actually better, but the only downside is likely cost.
And hopefully the study looking at the 3 mg dose, which is specifically looking at the impact of the 1.5 mg dose versus the 3 mg dose on ovulation, will be available later this year.
WHO Fact Sheet, Emergency Contraception https://www.who.int/news-room/fact-sheets/detail/emergency-contraception
Glasier A, Cameron ST, Blithe D, Scherrer B, Mathe H, Levy D, et al. Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel. Contraception. 2011 Oct;84(4):363-7.
Festin MP, Peregoudov A, Seuc A, Kiarie J, Temmerman M. Effect of BMI and body weight on pregnancy rates with LNG as emergency contraception: analysis of four WHO HRP studies.Contraception. 2017 Jan;95(1):50-54.
FSRH Clinical Guideline: Overweight, Obesity and Contraception (April 2019)
Emergency contraception, UpToDate. Author: David Turok, MD
International Consortium for Emergency Contraception. Clinical Summary: Emergency Contraceptive Pills. December 2018.