A cheap and widely available drug could save the lives of thousands of women who die in childbirth from excessive bleeding, one of the main killers of women worldwide.

The drug, tranexamic acid, is available over the counter in the UK to women suffering from heavy periods. In Japan and the far east, it is used as a skin whitener. But now a very large study of 20,000 women in 21 countries has shown it can stop a third of cases of bleeding to death after giving birth.

Haemorrhage after childbirth kills 100,000 women a year, mostly in low and middle-income countries. “It is not only the women dying – it is the impact on the child that has to grow up without a mother, children who might already be in the family and the husband,” said associate professor Haleema Shakur from the London School of Hygiene & Tropical Medicine who led the trial.

“This is of absolutely huge importance. While a single mother is dying, we need to keep fighting for them.”

The drug has already been proven to cut the death toll from bleeding after accidents in a trial of similar size. The latest trial, published in the Lancet medical journal, recruited more than 20,000 women who either gave birth in one of 193 hospitals involved or managed to get there after starting to bleed. They were randomly assigned either tranexamic acid or a placebo.

The researchers found that tranexamic acid was most effective when it was given soon after the bleeding began. The trial was originally intended also to find out whether the drug saved women from having to undergo a hysterectomy – the removal of the womb. But the scientists discovered that in many countries, where anaemia is common and blood supplies are limited, surgeons operated immediately as the surest way to save the woman’s life.

If all women who haemorrhage after childbirth were given the drug, the trial suggests that 30,000 lives could be saved a year. In practice, that will be more difficult. Tranexamic acid was given in an intravenous injection in the hospitals, as the quickest way to have an effect. Many women give birth at home and may not get to a hospital in time.

“It is available in the form of a tablet for heavy periods, but absorption may take too long,” said Shakur. They are now working on new ways to get it rapidly into women’s systems – perhaps as an injection in the arm muscle or as a capsule under the tongue. It is also possible that women deemed to be at high risk of haemorrhage could be given a tablet before they give birth. The trials have shown no side-effects, making the drug very safe.

Of the two-thirds of women who died in spite of being given the drug, Shakur said some arrived at hospital too late, while others had underlying illness including severe malaria and anaemia which may have been the cause of death.

It has taken a long time to show that the drug does work in the context it was designed for. Professor Ian Roberts from the London School, who co-led the study, said: “The researchers who invented tranexamic acid more than 50 years ago hoped it would reduce deaths from postpartum haemorrhage, but they couldn’t persuade obstetricians at the time to conduct a trial. Now we finally have these results that we hope can help save women’s lives around the world.”

There are many next steps, said Shakur. “We have to make sure tranexamic acid is available wherever a woman gives birth and is at risk,” she said. “We must make sure doctors and midwives are aware of the results of the study. And we need health ministers to make sure that the drug is available in their country and is on their shopping list of essential medicines.”