Cineole is the main constituent of eucalyptus oil, and it is mainly used as a mucolytic agent in inflammatory airway diseases. With its known mucolytic, bronchodilating, and anti-inflammatory effects, cineole reduces the exacerbation rate in patients suffering from chronic obstructive pulmonary disease. Based on these pharmacodynamic effects, we arrived at the hypothesis that asthma patients would benefit from concomitant therapy with cineole. As part of a double-blind, placebo-controlled, multicenter study, 247 patients with confirmed asthma were randomly selected according to the guidelines for this study. All patients were administered 200 mg of cineole, or a placebo, three times per day as a concomitant therapy over a period of 6 months. The combined primary outcome measures, which were implemented as a multiple criteria testing process, were improvement of lung function, asthma symptoms, and quality of life. Following the completion of the 6-month treatment period, it was noted that the patient group treated with cineole showed significantly more improvements to the multiple testing criteria than the patients in the placebo group (p = .0027). The statistical significance of the individual outcome measures could also be proven in accordance with the Wei-Lachin procedure (i.e., for Forced expiratory Volume 1 Second, p = .0398; for asthma symptoms, p = .0325; and for Asthma Quality of Life Questionnaire (AQLQ), p = .0475). Concomitant therapy using cineole can lead to notable improvement in lung function and health condition as well as to reduce dyspnea in asthma patients.