Hormonal contraceptives increase risk of breast cancer by one quarter, new study shows

The study of almost 30,000 women below the age of 50 tracked cases of the disease among those taking a range of contraception – including progestogen-only drugs, which have become increasing popular.

Use of such drugs has close to doubled in the past 20 years, with about three million women now taking them.

Meanwhile, the number of women on traditional combined pills has halved, leaving equal numbers now on each.

The popularity of the new generation drugs has partly been driven by hopes they would carry fewer health risks, with evidence suggesting they are less likely to cause strokes and blood clots.

But researchers found that progestogen-only drugs and coils carry at least equal risks as the combined pill, when it comes to breast cancer, in women below the age of 50. One in three women will be diagnosed with the disease over their lifetime.

However, experts cautioned that the majority of cases occurred above the age of 50 – saying the absolute risk of the disease remained “very small” in younger women.

Overall, the increased cancer risk for women taking progestogen-only drugs was 26pc, compared with 23pc for those on combined pills.

This rose to 32pc among those with progestogen-releasing intra-uterine devices, while those with hormonal implants experienced an increased risk of 25pc. Scientists stressed that the overall risks of breast cancer among young women remain low.

They said that the increased risk was “transient” – and largely disappears after stopping contraception.

Breast cancer is the most common cancer in Ireland, with about 3,400 cases annually.

Researchers said those taking hormonal contraception should take into account the increased risk of breast cancer, but said this would often be offset by other benefits of the drugs, including a long-term lowered risk of ovarian cancer and womb cancer, as well as their contraceptive function.

Women who took such pills for 15 years had a 2.2pc risk of breast cancer by their late 30s, against a 2pc risk among those who had not taken hormonal contraception. Among those in their late 20s, the risk rose from 0.5pc to 0.57pc.

Gillian Reeves, professor of statistical epidemiology and director of the Cancer Epidemiology Unit, Oxford Population Health, University of Oxford, said: “When the results from these studies were combined, we found a significant 20 to 30pc excess risk of breast cancer associated with each type.”

The study was published in PLOS Medicine.