Common contraceptive pill leaves women aged under 35 at greater risk of asthma attack

Women who take a certain type of contraceptive pill are at 40% higher risk of having an asthma attack, a study has shown.

Experts say the research could help us understand why asthma tends to be worse for women than for men. Researchers from Imperial College London found that taking the progesterone-only contraceptive pill was linked to an increased risk of asthma attacks in sufferers aged under 35.

The progestogen-only pill, or mini pill, is a daily oral contraceptive containing a synthetic version of the hormone progesterone. Unlike combined birth control pills, they do not contain the female hormone estrogen.

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Asthma and Lung UK, which funded the study, is calling for more research to examine the link between progesterone and asthma. The charity’s head of research Dr Erika Kennington said: "Historically little has been understood about why asthma is worse for women.

"This study is an important first step for women with asthma to better understand what lifestyle risks could increase their likelihood of an asthma attack. But much more research is needed to provide them with enough information to make more informed decisions on the best contraception choice for them.”

The study, published in the journal ERJ Open Research, examined data on 261,827 women aged between 18 and 50 who had been diagnosed with asthma and were taking the pill. They compared their data to 127,502 women with asthma who had not been prescribed an oral contraceptive.

Researchers then examined recorded asthma attacks among these women which occurred between 2004 and 2020. Women under the age of 35 who used the mini pill had a 39% increased risk of asthma attacks compared to never users. But there was no link among asthma attacks and older progesterone-only contraceptive pill users. Women taking fewer asthma treatments, such as inhaled or oral steroids, who were taking the progesterone-only contraceptive pill appeared to have a 20% increased risk.

Study lead Dr Chloe Bloom, a clinical senior lecturer in respiratory epidemiology at ICL’s National Heart and Lung Institute, said: "Asthma is common in women of reproductive age, many of whom are taking the pill. This study helps women and healthcare professionals make more informed decisions about which contraceptive pill might be best for them. The findings also add another piece to the puzzle of why women may be more likely to have severe asthma than men."

Professor Apostolos Bossios, head of the European Respiratory Society's group on airway diseases, asthma, COPD, and chronic cough, said: "We need much more research to understand why asthma is worse for women than men so we can begin to reduce the risk. This major study in an important step towards that aim."

Dr Erika Kennington added: "This research is still too early stage to change treatment decisions or prescribing guidelines and doesn't provide enough evidence for a prescriber to suggest to someone that they change their contraception pill. In the future, it would be beneficial for women to have the risk of an asthma attack considered alongside other health risks, such as heart disease and cancer.”

“This research highlights yet again the need for urgent action to increase investment into lung research to give everyone fighting for breath improved treatment options and a better quality of life."