OBJECTIVES: Decision aids (DAs) increase values-based decisions and the use of options that are beneficial to the patients but are underused. We assessed whether adding a DA to education enhanced decisional conflict and the appropriate use of pharmacotherapy among asthma patients. METHODS: We conducted a randomized parallel clinical trial. Educators randomly allocated adults with asthma who were prescribed inhaled corticosteroids (ICS) to the education or education + DA group. The DA presented information on ICS, compared their benefits and risks, and asked patients to weigh them. We measured decisional conflict, using the validated Decisional Conflict Scale (score 0–100, lower is better), and the use of pharmacotherapy, with an interviewer-administered questionnaire. We defined the appropriate medication usage according to 11 hierarchical criteria. Data were collected by blinded assessors at baseline and at two-month follow-up. Between the two time points, within- and between-group changes were estimated by linear mixed effects or generalized estimating equation model. RESULTS: Of the 51 randomized participants (response rate: 53%; age: 44 ± 13 years; women: n=32), 47 were included in analyses (education: n=23/25; education + DA: n=24/26). Between baseline and follow-up, the mean [95% CI] decisional conflict score decreased in the education group from 14.5 [8.1 to 25.4] to 5.7 [3.1 to 10.4] (P=0.01) and in the education + DA group from 10.4 [5.7 to 18.2] to 3.1 [1.4 to 5.9] (P=0.002). The proportion of participants who used their medication appropriately scaled up in the education group from 22% [10%–47%] to 39% [23%–65%] (P=0.10) and in the education + DA group from 46% [30%–71%] to 58% [42%–82%] (P=0.32) Improvements were no different between groups. CONCLUSIONS: Education improved decisional conflict whether the DA was added or not. The DA may be used during education interventions as a structure for discussion.