Morning after pill 'less reliable' for women over 11 stone

"Women who take morning-after pill could still fall pregnant if they weigh more than 11 stone," the Daily Mirror warns.

New guidelines on emergency contraception discuss recent evidence that body mass index (BMI) and overall body weight may impact on the effectiveness of oral emergency contraception.

The guideline – produced by the Faculty of Sexual Reproductive Healthcare – covers various recommendations around the type of emergency contraception that should be used in different circumstances. The aspect that has caught the media attention is that there is some uncertainty about the effectiveness of the commonly used morning after pill, Levonelle One in women who are overweight.

Who produced the guideline?

The Faculty of Sexual Reproductive Healthcare (FSRH) is a professional organisation of the Royal College of Obstetricians and Gynaecologists. It produces guidelines and training support for healthcare professionals to help them deliver the highest quality of sexual and reproductive healthcare.

The new guideline, Emergency Contraception, gives recommendations based on a systematic review of the available evidence, along with input from experts and the guideline development group.

What are the currently available forms of emergency contraception?

There are currently two forms of emergency contraception available – oral hormone tablets and the copper-containing intrauterine device or coil.

There are two hormone tablets. Levonorgestrel (brand name Levonelle One) is a single tablet that should ideally be taken within 12 hours of unprotected intercourse, but is effective up to 72 hours (three days).

The newer tablet, ulipristal acetate (brand name ellaOne) can be taken up to five days (120 hours) after unprotected intercourse.

Both are available on an over-the-counter basis.

The copper coil is believed to be more effective than the hormone methods and can be inserted into the womb up to five days after unprotected sex. It can also be used as an ongoing method of contraception.

However, if there's a chance the woman could have a sexually transmitted infection (STI) from having unprotected sex there can be a risk from inserting the coil, so antibiotics are usually given.

What does the new guideline recommend?

The guideline gives recommendations covering circumstances when emergency contraception may be needed (e.g. unprotected sex or possible failure or incorrect use of contraception) and the professional responsibilities of providers of emergency contraception (e.g. advising on need for ongoing contraception).

They then give data on the effectiveness of the different methods, confirming much of what is already known:

  • the copper coil is the most effective method
  • ellaOne is effective up to 120 hours
  • Levonelle One is effective up to 72 hours (evidence has shown it's ineffective after 96 hours)
  • ellaOne has been shown to be more effective than Levonelle One
  • the two hormone tablets are less likely to be effective if taken after suspected ovulation – in which case the copper coil is the preferred method

What do they say about weight or BMI

This is the main focus of the media coverage. The guideline covers two points on this:

  • Women should be informed that the effectiveness of the copper coil is not known to be affected by weight or BMI.
  • Women should be informed that it is possible that higher weight or BMI could reduce the effectiveness of oral emergency contraception, particularly Levonelle One.

If the woman weighs more than 70kg (11 stone) or has a BMI above 26kg/m2 (just above the 25 "threshold" for being overweight) and wants an oral method ellaOne is the recommended method. Ongoing hormonal contraception should then start after five days.

If Levonelle One is taken the new guideline recommends a double dose (3mg) as well as that the woman should start ongoing contraception immediately.

This is based on a systematic review of studies that have suggested that both hormone methods could be less effective in women who are overweight, obese or have higher body weight than those with normal or underweight BMI or lower body weight. Weight is thought to have a greater effect on Levonelle One than on ellaOne, hence the latter is recommended in preference. 

Other reasons oral emergency contraception may be ineffective

The FSRH also states that hormone tablets may not work if the woman is taking drugs that induce liver enzymes, such as epilepsy drugs. This warning also applies for the herbal remedy St John's Wort, which some people use to treat depression. In these cases women should use the copper coil in preference, or if not, a double dose of Levonelle One (though its effectiveness is unknown for this specific indication), ellaOne should not be used.

ellaOne can also be ineffective if progestogen-based contraception, such as the mini pill, is taken within five days of taking the tablet, and possibly if it was also taken in the seven days before ellaOne. ellaOne is also unsuitable for women who take steroids for severe asthma, and breastfeeding women should avoid breastfeeding or expressing for a week after taking ellaOne.


Overall the FSRH guideline gives additional clarity around the different types of emergency contraception that should be selected in different circumstances.

These recommendations are based on the best level of evidence and expert understanding to date. However, they may change in the future as more evidence comes to light.

In particular, related to the issue of weight on the effectiveness of oral emergency contraception, the European Medicines Agency (EMA) concluded in 2014 that the available evidence "was limited and not robust enough to support with certainty a conclusion that oral emergency contraception is less effective in women with higher body weight or BMI."

Still, as quoted in the Daily Mirror, the conclusion of Dr Asha Kasliwal, FSRH president, would seem a sensible one: "we hope its publication [the guidelines] will further awareness amongst healthcare professionals and women alike that the copper IUD is the most effective form of emergency contraception."

Read more about emergency contraception.

NHS Attribution