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Background: Patients with uncontrolled asthma should be evaluated for medication adherence. This study aimed to identify characteristics associated with poor adherence to inhaled corticosteroids (ICS) and to explore adherence prior to treatment escalation.

Methods: This nationwide longitudinal cohort study included adult asthma patients (n = 30880) with a healthcare visit including Asthma Control Test (ACT) and registered in the Swedish National Airway Register between 1 July 2017 and 28 February 2019 (index date). Patient data was crosslinked to other national registers. Treatment steps two years pre- and one year post-index, were identified by prescribed drugs. Poor adherence was defined as Medication Possession Ratio <80 %.

Results: Poor adherence was identified in 73 % of patients in treatment steps 2–5, where of 35 % had uncontrolled asthma (ACT≤19). In adjusted models, poor adherence was associated with better disease control; ACT≤19 (OR 0.78, 95 % CI 0.71–0.84), short-acting β2-agonist (SABA) overuse (0.69, 0.61–0.79) and exacerbations (0.79, 0.70–0.89) in steps 2–3. Among patients with uncontrolled asthma, poor adherence was associated with SABA overuse (1.71, 1.50–1.95), exacerbations (1.29, 1.15–1.46), current smoking (1.38, 1.21–1.57) and inversely associated with asthma management education (0.85, 0.78–0.93. Similar results were observed in steps 4–5. When investigating post-index treatment, 53 % remained stationary, 30 % stepped down and 17 % escalated treatment. Prior to escalation, 49 % had poor adherence.

Conclusions: Poor ICS adherence was associated with better asthma control. Among uncontrolled patients, poor adherence was associated with SABA overuse and exacerbations. Our result highlights the importance of asthma management education to improve adherence in uncontrolled patients.