A levonorgestrel-releasing intrauterine system holds promise as an alternative to the copper IUD for emergency contraception, a landmark US study suggests.

The hormone-eluting system has not been recommended for this indication because of a lack of data, researchers said.

Now, findings from a US randomised trial involving nearly 600 women (ages 18-35) who attended three Utah family planning clinics between 2016 and 2019, have shown the Mirena 52mg intrauterine system (IUS) is noninferior to the copper IUD for emergency contraception.

Just one of the 317 woman who had the hormonal device inserted within five days of unprotected sex returned a positive urine pregnancy test at the one-month follow-up, the researchers from the University of Utah reported.