FP (fluticasone propionate) is a synthetic fluorinated cortisol derivative with a strong anti-inflammatory effect. In inhaled form, it is used to treat asthma, and less frequently, to treat COPD. Typically the DPI inhaler used for administering dose of drug is provided in the standard medicine package. The use of a non-genuine inhaler to administer the medication into the respiratory track creates a risk of incorrect aerosolization of the dry powder containing FP. The aim of this study was to verify the correctness of action of the various commercially available inhalers in terms of dry powder aerosolization containing FP. To that reason, the analyses with the use of NGI were performed. The conducted research allowed to determine the Aerodynamic Particle Size Distribution (APSD), Fine Particle Fraction (FPF) and Fine Particle Mass (FPM). The quantitative determinations were made on the basis of the HPLC analytical method. The dry powder fractions distributed on the new generation impactor were collected using methanol. The samples were centrifuged and then filtered with a syringe filter into the chromatography vials. The FP content was quantified at each impactor level. The APSD plot was constructed and the FPF was calculated using the definite integral ranging from 1 to 5 µm. The conducted research has proven that various commercially available inhalers should not be used interchangeably. Moreover, the research showed that FPF decreases with the decrease in airflow velocity, which may have an impact on the therapeutic effect of the inhaled drug in people with low respiratory efficiency. The studies were financed by a grant from the National Centre of Research and Development, Poland, LIDER Program, No: LIDER/52/0276/L-12/20/NCBR/2021.