Your Emergency Contraception Might Not Work. Here’s the Real Reason.

The European manufacturer of NorLevo, an emergency contraceptive pill that’s identical to many of the most popular morning-after pills sold in the US, announced that they’ll be changing their packaging to warn consumers that it may not work for some overweight and obese women. The FDA has announced that they’ll review the data and decide whether or not to require a similar warning. A closer look shows that their numbers may not be 100% accurate, but unfortunately, this isn’t the only problem with EC pills containing this hormone. Read on to find out what the media’s getting wrong and what you need to know.

Packaging for Plan B One-Step
Do you need a Plan C? (Image courtesy

New NorLevo inserts state that “Studies suggest that Norlevo is less effective in women weighing 75 kg [165 lb.] or more and not effective in women weighing 80 kg [176 lb.] or more” and later says that Norlevo is not recommended for women weighing more than 75 kg. However, the University of Edinburgh, Scotland study that has been widely cited as the source of the data that led them to make these changes never actually mentions those numbers. Instead, it compares the outcomes of groups of women divided by BMI (kg/m²). BMI is dependent on height; a 165 lb. woman who’s 5’10” will fall into the “normal” range, while a 5’2″ woman at that weight is considered “obese” by the same calculation. Neither of them would have fallen into the “overweight” category in the study that showed that the pill was losing effectiveness; in theory the pill should work on the taller woman and not on the shorter one, though the packaging (and the vast majority of reporting on the story) doesn’t distinguish between the two. And of course, BMI alone isn’t really an effective tool to evaluate how different people will be affected by drugs since it doesn’t take into account differences in muscle mass v. body fat percentages. Presumably, these numbers were chosen to represent an average height woman, but they’re by no means set in stone. There’s no magic diving line at those weights that automatically renders the pill less effective or totally useless.

So what did they actually find? The study compared outcomes for women taking pills containing levonorgestrel (LNG) and ulipristal acetate (UPA). ECs with LNG are available without a prescription and in certain instances over-the-counter; they include Plan B One-Step, Next Choice One Dose, My Way, and some generics that still have two pills. UPA is available by prescription only and is marketed as EC under the name Ella. UPA showed a lower failure rate than LNG in every category, though it did still fail more often in obese women (2.6% of those studied got pregnant) than in overweight, normal, or underweight women (1.1%). LNG failed in 1.3% of normal and underweight women, 2.5% of overweight women, and 5.8% of obese women. This fell slightly above the study’s assumed pregnancy risk of 5.6% for any random act of unprotected sex that isn’t followed by EC, but is still far lower than the 30% chance of pregnancy for sex during the most fertile time of the month. Anecdotally, women are more likely to seek out EC if they think they’re close to ovulation than if they’re at the beginning or end of their cycle, so it’s possible that the LNG did prevent some pregnancies in obese women. (In other words, the 94.2% of obese women who took LNG and didn’t get pregnant most likely weren’t going to get pregnant even without taking EC, but it might have made a difference for a few and there’s no real way to know which ones.)

The study was not able to draw any conclusions as to why the pills would affect overweight women differently, as they were only studying the failure rates between groups under various conditions, not the physical mechanisms that led to success or failure on an individual level. Many studies have found that the effectiveness of various oral birth control methods can vary based on weight or BMI, though the exact reason is not known. However, injectable and implantable birth control options have little difference in failure rates based on weight or mass. LNG is present in many of these contraceptives in lower doses than in EC, so it makes sense that the failure rates would be similarly linked to weight/mass, though further study is needed.

Unfortunately, this isn’t the only problem with EC pills containing LNG. LNG is a synthetic hormone which acts to inhibit ovulation. While the product labeling may contain claims that these products can also stop a fertilized egg from implanting, a 2011 statement from the International Federation of Gynecology & Obstetrics (FIGO) says multiple studies have found evidence that this is not actually the case and that these labels should be changed. The same report says it’s inconclusive as to whether levonorgestrel can affect sperm function at the dosage level in EC pills, so it may not prevent fertilization as advertised either.

What can we take away from all this? A report released this month by Princeton concluded that:

Emergency contraception provides women with a last chance to prevent pregnancy after unprotected sex. Women deserve that last chance, and barriers to availability should be eliminated. But it is unlikely that expanding access will have a major impact on reducing the rate of unintended pregnancy, primarily because the incidence of unprotected intercourse is so high, ECPs are only moderately effective, and ECPs are not used often enough.

All this doesn’t mean that you should skip the EC if you have unprotected sex, even if your BMI categorizes you as overweight or obese. It does mean that you may want to be more diligent about practicing safe sex and finding a long-term contraception method that works for you and your partner(s). If you do have unprotected sex and want to get EC without a prescription, don’t delay. Even though they advertise that they should be taken within a 72 (or in some cases 120) hour window, you need to act as quickly as possible to prevent ovulation, because once the egg is out there, LNP won’t protect you from fertilization or implantation. Most sperm in your uterus will die within a day or two anyway, though under the right circumstances some may survive for up to 5 days, so you may still prevent pregnancy by taking it later if you haven’t ovulated yet. Both studies recommended the insertion of a copper IUD to have the greatest odds of preventing implantation, especially when the unprotected sex occurred mid-cycle, but they acknowledged that it may be difficult to have the procedure performed quickly enough to prevent pregnancy and that some women may not want a relatively permanent solution to a one-time failure. (The cost can be prohibitive as well.) None of this, however, means that the pills shouldn’t be available over-the-counter or that younger women should be banned from buying it without a prescription. Sadly, you don’t have to look too hard to find people espousing this view already, but it’s not like most doctors would have necessarily known about the difference at all before the story hit the news this week, and until further studies are done, we shouldn’t be discouraging people from taking EC based solely on their weight. We just don’t know enough yet.


By [E] Hillary

Hillary is a giant nerd and former Mathlete. She once read large swaths of "Why Evolution is True" and a geology book aloud to her infant daughter, in the hopes of a) instilling a love of science in her from a very young age and b) boring her to sleep. After escaping the wilds of Waco, Texas and spending the next decade in NYC, she currently lives in upstate New York, where she misses being able to get decent pizza and Chinese takeout delivered to her house. She lost on Jeopardy.

7 replies on “Your Emergency Contraception Might Not Work. Here’s the Real Reason.”

I found this an informative post as well:
Levonorgestrel methods, like Plan B, are significantly less effective for women with a BMI of 30 or more. A copper IUD within 5 days of unprotected intercourse will offer the best method of post coital contraception for women regardless of BMI and for women with a BMI over 30, and Ella is the second choice based on efficacy.

It might be a good idea to get a prescription for Ella (the UPA morning after pill) from your doctor to have on hand

I am a proud member of the Paragard tribe but I like how they just all assume every woman can afford an IUD. I lucked out because I was young enough to be covered by my mother’s insurance and got a discount. But that was still almost $300.

Hm. This whole time I’ve been calling the Mirena and IUD instead of an IUS. When I read your response, I immediately ran to google thinking “What is this IUS? I must know of this!” You learn something new everyday. Now I shall go properly armed into the world, continuing to spread of the gospel if IUDs and IUSs!

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