In patients with COPD, a relationship between breathlessness and respiratory effort, assessed in terms of mouth occlusion pressure (P0.1), has been described. To evaluate the short-term effects of inhaled terbutaline on breathlessness, breathing pattern, and P0.1 in patients with nonreversible COPD, we designed a randomized, double-blind, parallel, placebo-controlled study. Twenty-five patients with stable nonreversible COPD, mean age 64 +/- 11 years, were enrolled in the study. Patients received 500 micrograms inhaled terbutaline or placebo. Breathlessness, using the Borg scale, breathing pattern, and P0.1 were measured at baseline and 30 min after inhalation. Terbutaline resulted in a significant decrease in Borg scale, while no differences were observed after placebo. No significant changes in breathing pattern were found. Nevertheless, a decrease in P0.1 (0.31 +/- 0.07 vs 0.21 +/- 0.05 kPa; p < 0.001) after terbutaline inhalation was observed. Borg score was correlated with P0.1 in all patients. Moreover, changes in Borg score after medication were directly proportional to P0.1 changes (r = 0.85; p < 0.01). We conclude that terbutaline decreases central inspiratory drive and improves breathlessness in patients with nonreversible COPD.