Research found that protection can last for 30 years after use has stopped, with every five years of taking the pill reducing chance of womb cancer by a quarter

The pill not only prevents pregnancy but protects women from two forms of cancer for decades after they have stopped using it, say leading experts.

Oxford University researchers say in the past 10 years, taking the pill has prevented 200,000 cases of womb cancer in high-income countries. In 2008, the Oxford epidemiologists, analysing the data from 45 studies involving 100,000 women, found that regular use for 15 years can halve the risk of ovarian cancer.

In both cases, the protection can last for more than 30 years, long after women have stopped using contraceptives. Women in their 70s who took the pill in their youth are still enjoying its protection, says Prof Valerie Beral, lead author of the new study on the pill and endometrial (womb) cancer in the Lancet Oncology journal.

“There are two conditions where we have this really big effect that is long-lasting,” said Beral. “There is an increase in cancer of the breast and cervix, but it is really quite small and they don’t persist.” Once a woman stops taking the pill, her increased chances of breast or cervical cancer quickly disappear.

“What it means is that women in their 50s and 60s who took the pill are less likely to get cancer than women who did not, and the longer they have taken it the less likely they are. That is pretty important.

“It is time to start saying that not only does it prevent pregnancy, which is why people take it, but you should know you are less likely to get cancer than women who don’t take the pill.”

But, she added, she knew it would not be a popular message. “People [almost] don’t want to believe it,” she said.

The paper found that the longer women took the pill, the greater the protection from endometrial cancer they enjoyed. The researchers estimated that from 1965 to 2014, 400,000 cases of endometrial cancer have been prevented in high-income countries, including 200,000 in the last decade.

The researchers examined data from 36 studies on 27,276 women with endometrial cancer from North America, Europe, Asia, Australia, and South Africa – virtually all the epidemiological evidence ever collected on the effect of oral contraceptives. The study was funded by the Medical Research Council and Cancer Research UK.

They found that every five years of oral contraceptive use reduces the risk of endometrial cancer by about a quarter.

In the 1960s, the pill contained more than double the oestrogen level than it did by the 1980s, but the protection from endometrial cancer was the same even for women taking lower dose pills.

Beral said that the overall numbers of women with endometrial cancer would have dropped further if it had not been for obesity, which increases the risk.

In a commentary in the journal on the paper, Nicolas Wentzensen and Amy Berrington de Gonzalez,from the National Cancer Institute in the US, say that the important question now is whether this allows women to better balance the benefits and the potential harms of taking the pill - and also to work out whether the pill might be useful in some circumstances specifically to prevent cancer.

There is still a risk of blood clots, they point out, and different versions and doses of the pill carry different risks of stroke and heart attack. How and why the pill carries some risks and other benefits is not well understood.

“Even if the biological mechanisms remain elusive and the existing evidence falls short of wider recommendations for [prescribing the pill to prevent cancer], women need to be more aware of the unintended benefits and the risks of oral contraceptives, so that they can make informed decisions,” they conclude.

