Contraceptives used by millions of women may significantly increase the risk of developing a common type of brain tumour, a major study suggests.
Danish researchers analysed the health records of three million women over 25 years and found that pills, injections and coils containing the hormone progestogen were associated with a significantly increased risk of meningioma.
This is usually non-cancerous tumour that develops in the tissues surrounding the brain and spinal cord.
Meningiomas are the most common type of brain tumour, accounting for more than a quarter of cases diagnosed in Britain and around 3,000 new cases each year.
While most are benign, they can cause headaches, seizures and vision problems as they grow and press on nearby tissue, sometimes requiring surgery or radiotherapy.
The strongest association was seen with one commonly used contraceptive injection, which was linked to a 355 per cent increase in the risk of developing a meningioma.
Previous studies have also suggested a link between progestogen-based medications and the tumours, which are known to occur more frequently in women than men.
Experts said the findings should help inform discussions between doctors and patients about the benefits and risks of different contraceptive options.
Some contraceptive pills, jabs and coils may put women at a greater risk of developing brain tumours, a major study has found
The study, published in JAMA Network Open, analysed health records from three million women aged 15 to 59 over a 25-year period.
Researchers compared 1,473 women diagnosed with meningioma with 14,717 women who did not have the tumour and found the strongest association among users of the contraceptive injection medroxyprogesterone.
Women using the drug, which is sold in Britain as Depo-Provera, had 355 per cent higher odds of developing a meningioma than those who did not take it.
The risk was highest among older women.
Among those aged 55 to 59, researchers estimated there was one additional case of meningioma for every 5,372 women using the injection for a year.
By comparison, among women aged 15 to 19, there was one extra case for every 449,000 users.
The researchers also found increased odds of meningioma among users of several combined contraceptive pills containing both oestrogen and progestogen.
The highest increase was linked to desogestrel, which was associated with a 66 per cent rise in odds, followed by cyproterone (61 per cent), drospirenone (58 per cent), gestodene (44 per cent), levonorgestrel (40 per cent), norethisterone (38 per cent) and norgestimate (4 per cent).
The NHS says natural family planning can be up to 99 per cent effective when done correctly and around 75 per cent if not used according to instructions. By comparison, the Pill, implant, IUS and IUD are 99 per cent effective with perfect use, while condoms are 98 per cent
Levonorgestrel and norethisterone are among the most widely used progestogens in contraception and feature in popular brands including Microgynon, Rigevidon and Brevinor.
Among women taking progestogen-only contraceptive pills, often known as mini pills, desogestrel was associated with a 73 per cent increase in the odds of developing meningioma. No significant increase was seen among users of norethisterone-only pills.
Desogestrel is one of the most commonly prescribed mini pills in Britain and is sold under brand names including Cerazette and Cerelle.
The researchers also found that women using intrauterine devices (IUDs) containing high-dose levonorgestrel had 58 per cent higher odds of developing meningioma. However, no increased risk was seen with lower-dose levonorgestrel coils.
Writing in JAMA Network Open, the researchers from the Danish Medicines Agency said the findings suggest the risk of meningioma may extend beyond high-dose progestogen treatments and depot medroxyprogesterone injections to include some commonly used contraceptive progestogens.
Reassuringly, the study found the increased risk generally disappeared within five years of women stopping the contraceptive.
The researchers were unable to draw firm conclusions about several other progestogen-containing contraceptives because too few women had used them or too few cases of meningioma occurred during the study period.
These included etynodiol, lynestrenol, nomegestrol, dienogest, norelgestromin, drospirenone-only pills, levonorgestrel-only pills and etonogestrel implants and vaginal rings.
The study also found no clear increase in risk among users of the combined pill containing norgestimate, the progestogen-only pill norethisterone or low-dose levonorgestrel coils.
Experts not involved in the research welcomed the findings but stressed that the overall risk to individual women remains low.
Professor Paul Pharoah, a cancer epidemiologist at Cedars-Sinai, said: 'Importantly, they found that this risk only persisted while women were using the hormonal contraceptive and declined once they stopped.
'This is an observational study and proving the association is causal is difficult because it is impossible to rule out all potential confounding factors. However, given the available evidence, a causal link appears likely.'
Professor Channa Jayasena, a reproductive endocrinologist at Imperial College London, added: 'All medications carry risks and contraceptive medicines are no different. As the paper correctly states, the overall chance of these drugs causing a meningioma is tiny.'
Associate Professor Gino Pecoraro, an obstetrician and gynaecologist at the University of Queensland, said the findings highlighted the importance of discussing both risks and benefits when choosing contraception.
He added that women concerned about the findings could consider alternatives that do not contain progestogens, such as barrier methods or copper coils, after consultation with their healthcare provider.
