The Pill brings mixed tidings

The contraceptive pill has effects on women’s health – some good, some bad, researchers warned today.

Firstly, Professor Ojvind Lidegaard of the University of Copenhagen, Denmark, found that some oral contraceptive pills are more likely than others to cause serious blood clots (venous thromboembolism, or VTE). This confirms previous findings.

Details were gathered from all Danish non-pregnant women between the ages of 15 and 49 from January 2001 until December 2009.

Women taking pills containing one of the newer types of progestogen hormone (drospirenone, desogestrel or gestodene) had double the risk of VTE than women on pills containing an older progestogen (levonorgestrel).

Reporting in the British Medical Journal, the authors say that the risk of VTE is still low, at about ten per 10,000 women years for newer pills. It would take about 2,000 women changing to older pills to prevent one case of VTE a year, they calculate.

Dr Philip Hannaford of Aberdeen University, UK, comments: "Many clinicians will choose to minimise the risk by prescribing a combined oral contraceptive with levonorgestrel whenever possible."

In the second study, Dr Naomi Allen of Oxford University, UK, and her team looked at the risk of ovarian cancer. They found that taking the pill for more than ten years was the biggest factor linked to reduced risk of developing the disease.

The next biggest factors linked to reduced risk is undergoing pregnancy and having more than one child.

For women who took the pill for a year or less, the risk of ovarian cancer was about 28 per 100,000 women per year. But for those who took it for at least ten years, the risk was about around 15 per 100,000 per year.

This benefit is balanced against a slightly increased risk of developing breast cancer, say the authors. Details are published in the British Journal of Cancer.

Scientists do not know the reasons for the links they have found. There could be underlying lifestyle factors, such as sexual activity – or hormonal factors linked to taking the pill and having children.

Researcher Naomi Allen, of Oxford University, UK, said: “Ovarian cancer is difficult to detect and so prevention is key to saving women suffering from this disease. These results are important because most women don’t know that taking the Pill or getting pregnant can help reduce their risk of ovarian cancer later on in life."

And Dr Richard Edmondson, a Cancer Research UK expert based at Newcastle University, said: "Women may be reassured to know that the oral contraceptive is not only an effective contraceptive but can have the added benefit of reducing their risk of ovarian cancer.

"This is however balanced against a slightly increased risk of developing breast cancer. To put this in context, it is estimated that if 100,000 women use the pill for ten years or more there will be 50 more breast cancers than would have otherwise occurred, but 12 fewer ovarian cancers."

Lidegaard, O. et al Risk of venous thromboembolism from use of oral contraceptives containing different progestogens and oestrogen doses: Danish cohort study, 2001-9. The British Medical Journal, 2011;343:d642.

Hannaford, P. C. The progestogen content of combined oral contraceptives and venous thromboembolic risk. The British Medical Journal, 2011;343:d6592.

Oral Contraceptive Use and Reproductive Factors and Risk of Ovarian Cancer in European Prospective Investigation into Cancer and Nutrition.Konstantinos, K. et al. British Journal of Cancer, published online October 26, 2011.