Hormonal contraceptives are associated with an increase in incidence of asthma in women.

Abstract

Use of exogenous female sex hormones is associated to development of asthma, but the question of whether the effect is protective or harmful remains unresolved. To investigate whether initiation of hormonal contraception was associated with development of asthma. We performed a register-based, exposure-matched cohort study including women who initiated hormonal contraceptive treatment of any kind between 10 and 40 years of age and compared the incidence of asthma with women who did not initiate hormonal contraceptives. Asthma was defined as two redeemed prescriptions of inhaled corticosteroids within two years. Data were analysed using Cox' regression models adjusted for income and urbanization. We included 184.046 women with a mean age of 15.5 years (SD 1.5), where 30669 initiated hormonal contraceptive treatment and 153377 did not. We found that initiation of hormonal contraceptives was associated with an increased hazard ratio of developing new asthma by 1.78 (95%CI 1.58-2.00; P<0.001). The cumulative risk of new asthma was 2.7% after three years among users of hormonal contraceptives compared to 1.5% in non-users. In the different subtypes of hormonal contraceptives, 2nd and 3rd generation contraceptives carried significant associations (second generation HR 1.76; 95%CI 1.52-2.03; P<0.001 and third generation HR 1.62 95%CI 1.23-2.12; P<0.001). The association with increased incidence was only seen in women below 18 years. In this study, first-time users of hormonal contraception had an increased incidence of asthma compared with non-users. Clinicians prescribing hormonal contraceptives should be aware that airway symptoms may develop.