The efficiency of lung drug delivery of nebulized drugs is governed by aerosol quality, which depends both on the aerosolization process itself but also on the properties of aerosol precursors. This paper determines physicochemical properties of four analogous micro-suspensions of a micronized steroid (budesonide, BUD) and seeks relationships between these properties and the quality of the aerosol emitted from a vibrating mesh nebulizer (VMN). Despite the same BUD content in all tested pharmaceutical products, their physicochemical characteristics (liquid surface tension, viscosity, electric conductivity, BUD crystal size, suspension stability, etc.) are not identical. The differences have a weak influence on droplet size distribution in the mists emitted from the VMN and on theoretical (calculated) regional aerosol deposition in the respiratory system but, simultaneously, there is an influence on the amount of BUD converted by the nebulizer to aerosol available for inhalation. It is demonstrated that the maximum inhaled BUD dose is below 80–90% of the label dose, depending on the nebulized formulation. It shows that nebulization of BUD suspensions in VMN is sensitive to minor dissimilarities among analogous (generic) pharmaceutics. The potential clinical relevance of these findings is discussed. Keywords: nebulization; aerosol; budesonide; vibrating mesh nebulizer; physiochemical characteristics