Twenty years of inhaler therapy: A nationwide drug utilization study.

AIMS: This study aimed to map nationwide trends and prescribing patterns in inhaler use from 2004 to 2023. In light of evolving clinical guidelines and attention to the environmental impact of inhalers within recent years, we also examined variation in prescribing behaviour and patient-level treatment choices. METHODS: Using nationwide health registries, we identified all individuals redeeming prescriptions for pressurized metered-dose inhalers (pMDIs), dry powder inhalers (DPIs) and soft mist inhalers (SMIs) in Denmark over the past 20 years. Analyses included trends in total use, new and chronic use, patient demographics, comorbidities, markers of disease severity and prescribing sector. Subgroup analyses stratified use patterns by inferred diagnosis (asthma vs. COPD) and repeated main analyses excluding children <6 years. RESULTS: From 2004 to 2023, total inhaler doses increased by 15%, driven primarily by a 62% rise in pMDI use. The pMDI share of the total doses grew from 29% to 42%. New pMDI users increased by 34%, while long-term pMDI users nearly doubled (93%). DPI use declined slightly. pMDI and SMI users had higher rates of exacerbations and prednisolone use compared to DPI users. More than 90% of inhalers were prescribed in primary care. CONCLUSIONS: pMDI use in Denmark has increased substantially over the past two decades, particularly among long-term users. These findings highlight a complex interplay of clinical, behavioural and systemic factors influencing inhaler choice. As clinical guidelines evolve and awareness of inhalers' environmental impact grows, targeted strategies are needed to optimize prescribing practices for both improved patient outcomes and climate sustainability.