Women who take a painkilling tablet alongside the world’s most widely used morning-after pill have a far smaller risk of becoming pregnant than those who rely on emergency contraception alone.
Sexual health experts have hailed the finding, reported on Thursday in the Lancet, as a significant and “very exciting” potential breakthrough that could make it easier to prevent pregnancy after unprotected sex.
Governments and health services should consider changing their clinical practice policies so that women who want to avoid becoming pregnant are routinely offered both drugs, they said.
Taking piroxicam, an anti-inflammatory drug usually used to treat arthritis, at the same time as the morning-after pill levonorgestrel prevents 95% of pregnancies in such circumstances, according to a randomised controlled trial undertaken by medical academics in Hong Kong and Sweden.
In comparison levonorgestrel on its own, in conjunction with a placebo, only managed to prevent 63% of pregnancies.
The combined treatment “prevents significantly more pregnancies compared to taking levonorgestrel alone”, the authors of the study found.
Levonorgestrel is one of the two pills most widely used as emergency contraception worldwide. The other is ulipristal acetate, which is used in fewer countries.
Both work by preventing or delaying ovulation and neither is effective after ovulation has occurred.
Dr Sue Lo, a co-investigator of the study, who works at the Family Planning Association of Hong Kong, said: “The levonorgestrel emergency contraceptive pill is one of the most popular choices of emergency contraception in many parts of the world, so finding out that there is a widely available medication which increases levonorgestrel’s efficacy when they are taken together is really exciting.”
Women can take either of the morning-after pills to avoid a pregnancy when they have had sex without using contraception or when their contraception has failed, such as when a condom breaks.
Lo and colleagues undertook the trial among 860 women who accessed levonorgestrel emergency contraception at a sexual and reproductive health service in Hong Kong between 2018 and 2022. In all 418 women were given a single 1.5mg dose of the drug plus either 40mg of piroxicam while another 418 were given the morning-after pill and a placebo.
The combination of drugs prevented 95% of pregnancies whereas levonorgestrel on its own only led to pregnancy being avoided in 63% of women that took it. There was no difference between the two groups in the side effects they experienced, such as having a late period, which causes anxiety.
A trial in 1998 found that levonorgestrel on its own was 95% effective at preventing a pregnancy if taken within 24 hours after unprotected sex, 85% effective 25 to 48 hours later and 58% effective if used 49 to 72 hours later. However, more recent research has cast doubt on those levels of success.
The study “has the potential to improve the efficacy of emergency contraception, which is very exciting”, said Dr Janet Barter, the president of the Faculty of Sexual and Reproductive Healthcare, which represents those working in sexual health services in the UK.
Richard Anderson, the Elsie Inglis professor of clinical reproductive science at Edinburgh University, said the study had shown “a big difference in effectiveness” between the two drug regimes and that the combination is “easily and cheaply translatable into normal clinical practice, although only with this specific drug”.
However, Dr Erica Cahill, from Stanford University’s medical school, said the study’s findings might not apply to women everywhere, because participants were all Asian, or to people with a high body mass index, as women involved generally weighed less than 70kg.