Fitting a copper IUD within 5 days of unprotected sexual intercourse is a very effective means of postcoital or emergency contraception. A single dose of the progestin contraceptive levonorgestrel, administered within 4 days of unprotected sexual intercourse, is the drug of choice for this indication. Another option is a 30 mg dose of ulipristal, given within 5 days of unprotected sexual intercourse, but its history of use is not as well established as the other two methods.

Some studies appear to show that levonorgestrel and ulipristal are less effective in women weighing 75 kg or more. Other studies have not shown this risk with levonorgestrel: the European Medicines Agency (EMA) deemed the evidence insufficient to modify the patient information leaflet, contrary to the French health products safety agency.

In practice, when emergency contraception is required, a single 1.5 mg dose of levonorgestrel or a 30 mg dose of ulipristal are possibly less effective in cases of obesity or even in women who are simply overweight.

The most reasonable option then is to warn overweight or obese women seeking emergency contraception and offer, when possible, to fit a copper IUD within 5 days of intercourse, since there is no evidence that this is less effective in cases of excess weight. As well as being more effective, this option has the benefit of combining emergency and long-term contraception.

©Prescrire 1 December 2014

"Emergency contraception in overweight women: an IUD is preferable" Prescrire Int 2014; 23 (155): 300-301. (Pdf, subscribers only).