OBJECTIVES: To demonstrate Rx data application in relation to comparative effectiveness of inhaled corticosteroids (ICS) through evaluation of the rate of adherence to drug therapy and consumption of rescue medications in respiratory impaired patients.    METHODS: Participants: A total of 533,382 patients age 18 or older who filled a prescription for ICS drugs. Setting: More than 12,153 community pharmacies nationwide. Data were from computerized pharmacy records. Design: The persistency analysis included prescription data for ICS dispensed during a 4-month period. Patient prescription activity was followed for 360 days. Patients were monitored for consumption of short acting beta agonist (SABA) medication in combination with their index ICS for 360 days from their ICS index fill date. An average SABA consumption in days for each index ICS drug was calculated.  RESULTS: Persistence with ICS is generally poor; about 60% to 78% of patients drop off therapy within the first 30 days of therapy. Fluticasone/salmeterol (F/S) combination shows the best persistence and budesonide the worst persistence. Children were more persistent with mometasone whereas patients 19-60 and 60+ were more persistent with F/S. Budesonide and triamcinolone had the worst persistence with all age groups. The same results were seen in patients with multiple co-morbidities. Persistency with ICS across different co-morbid condition was consistent. On average 67% to 91% of ICS users took a SABA concomitantly. Budesonide (N=69,432) patients on average used fewer days of SABA therapy (higher control), whereas budesonide/formeterol combination (N=25,763) patients used more days of SABA therapy (lower control). CONCLUSIONS: Rx data can be used to compare effectiveness of drugs in a class across different population segments. Our analysis showed that different ICSs have different effectiveness, as indicated by the rate of adherence to therapy and use of rescue medication, in different individuals.