BDNF and chronic obstructive pulmonary disease: Although we did not find significant differences in BDNF concentrations between patients treated with antidepressants, roflumilast or oral corticosteroids and those patients not treated with these drugs, our study was clearly underpowered to draw any firm conclusions on the influence of different classes of antidepressants, roflumilast or oral corticosteroids on BDNF serum concentrations in patients with COPD.