The Faculty of Sexual and Reproductive Healthcare (FSRH), of the Royal College of the Obstetricians and Gynaecologists in the UK has said the pill can fail for women with a body-mass index (BMI) of over 26 or in those who weigh 11 stone (70kg) or more.

The notice is part of a guideline on emergency contraception published in March, which urges doctors and pharmacists to explain the risks to larger women.

Drug diluted in bloodstream lowers effectiveness

Dr Jane Dickson, vice president of the faculty said, “We believe there is evidence to suggest that in heavier women, the drug may be less effective because the drug is diluted in their blood stream.”

The news is likely to be alarming for many, given that more than half of UK women are thought to weigh more than 70kg. However, Dickson added that “the 11 stone figure is based on research. It is something of an arbitrary figure and it may be 15 stone (95kg) is the danger point for some women.”

“But for safety 11 stone or a BMI over 26 is the level we can say weight may create a risk,” she explained.

The advice comes from a 2016 review, conducted by the Division of Reproductive Health in the US Centers for Disease Control and Prevention, of studies on the safety and effectiveness of emergency contraceptive pills among women with obesity.

Contraception effectiveness and weight not a new issue

The link between weight and the morning-after pill's effectiveness has been raised in previous studies but has proved controversial. The issue first came to light in 2012, when an Edinburgh University study found that obese women were more than three times as likely as those of normal weight to become pregnant after taking the emergency contraceptive pill.

In 2013, the European Medicines Agency forced the makers of levonorgestrel-based pills to add a warning to its packaging that the product might be less effective for overweight women. Following a review however, the agency had changed its mind and in 2014 said it is suitable for heavier women.

Last July, a small study involving 10 participants found the amount of the hormone present in overweight women was 50% less than in their lighter counterparts, meaning there was an increased risk of pregnancy.

Doctors should encourage women to find better forms of contraception

The FSRH said pills containing ulipristal acetate and levonorgestrel, the two most common forms of emergency contraceptive pills, are affected by weight. Between the two, levonorgestrel-based pills are believed to be less effective on heavier women.

Marketing manager for HRA Pharma, which manufactures ulipristal acetate pills, Clare Newins, said that women should not misunderstand the new guidance and wrongly believe that there are no suitable oral emergency contraceptive options available to them.

“It continues to be the most effective oral option for most women at the standard dose regardless of their weight or BMI,” she added.

Larger women can be advised to take two emergency contraceptive tablets, or use an emergency coil instead. FSRH recommends health professionals to advise women that the coil is the best emergency contraception. Trials have suggested that the failure rate for the intrauterine device (IUD) as an emergency contraception is lower than 1%.

However, research reveals that 95% of women are issued the emergency contraceptive pill when obtaining emergency contraception, probably due to the convenience of visiting a pharmacy, whereas an IUD must be fitted by a health professional at a GP surgery or a sexual health service.

Dickson said, “The coil's effectiveness is not affected by a woman's weight as it works differently to prevent fertilisation. And weight issues aside, it is more effective than the morning-after pill.” MIMS

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