Aerosol drugs are effectively used to treat chronic respiratory diseases. The efficiency of the therapy depends also on the amount and distribution of drug deposited within the airways. The objective of this study is to apply numerical techniques to analyse the effect of the duration of breath-hold after the inhalation of six different commercialized dry powder drugs on their lung deposition. For this purpose a computational airway deposition model has been adapted and validated to the special case of therapeutic aerosols. Our results show that lung dose of the studied drugs can be enhanced by 11.3%–26.5% with a 5 s breath-hold and by 20.7%–53% with a 25 s breath-hold compared to the no-breath-hold case. Although this later duration may not be achieved by COPD patients, present results clearly show the importance of holding the breath as long as possible. Current computations also revealed that there is a strong positive correlation between the enhancement of lung dose as a result of breath-hold and the amount of fine particles in the drugs. Present tendencies aiming at producing drug particles of smaller and smaller sizes will lead to the further enhancement of the importance of producing a sufficiently long breath-hold time after the drug inhalation. In addition, higher lung deposition will be possible by the more correct use of inhalation devices, more precise and detailed patient information materials and personalized drug choice and therapy.