Objectives The aim of this paper is to describe biopharmaceutical peculiarities of inhaled medicinal products and contribute to the understanding of guidelines for preparation of documentation for marketing authorization laid down by the European Medicines Agency (EMA), which are related to drug development, production, quality control and stability testing. Materials and Methods Literature search was done by topic and subject of research, authors and journals, from general to specialized articles and guidelines relevant to the issues of this paper. The targeted search was carried out via the on-line databases such as ScienceDirect, PubMed, medicinal products database of the Agency for Medicinal Products and Medical Devices of Croatia. The regulatory guidelines have been detailed searched through the European Medicines Agency database. Results Inhalation drug products have been widely accepted for localized treatment for pulmonary diseases such as asthma and chronic obstructive pulmonary disease and they are available for over 50 years in the market. It is a major interest of the pharmaceutical industry to develop inhalation drug products due to the large number of patients suffering from asthma and chronic obstructive pulmonary disease. For local activities, the orally inhaled drugs are delivered directly to the site of action in the lung, providing fast onset action within 5 minutes. The advantage of these drugs products is the route of administration, directly in the lower respiratory tract where the active substance has effect at relatively low doses, while at the same time the systemic absorption of the drug is minimal, thereby reducing the possible side effects of the drug. By using the inhalation drug product, the first pass metabolism through the liver is avoided, the drug action is provided directly to the site of action, and systemic side effects are avoided. Inhalation drug products are commonly classified into three categories: pressurized metered dose inhaler (pMDI), dry powder inhaler (DPI) and nebulizer. All these inhalation drug products are a combination of formulation and device. The formulation is designed to provide intended efficacy for patients, and to achieve this goal, it needs to be compatible and works together with a device. An inhalation product should be able to provide consistent dose content, along with suitable aerodynamic particle size distribution, to ensure that the drugs can be efficiently delivered to the target sites in the lung. A well designed inhaler must also consider its usability for patients use in terms of features such as robustness, ease of use, portability, and suitability for all ages in order to achieve good patient compliance with the technique instructions. Each type of inhaler has its specific formulation, device and clinical advantages. Conclusion Application for granting marketing authorization for inhaled medicinal products in EU can be submitted according to Article 8(3) of Directive 2001/83/EC (full dossier) or according to Article 10(3) of Directive 2001/83/EC (hybrid application). The greatest challenge in the development of generic / hybrid inhaled medicinal products is the demonstration of therapeutic equivalence between two inhaled products. Therapeutic equivalence should be demonstrated by means of appropriate clinical studies when equivalence is not shown according in vitro requirements and if it is not shown convincingly by investigation of systemic safety and pulmonary deposition. Clinical studies are conducted to examine the efficacy and safety of the inhaled medicinal product and should be based on the safety results obtained in previous clinical studies as well as data obtained in non-clinical studies. Exclusion of clinical studies is justified in cases where the hybrid inhaled medicinal product compared to the reference product satisfies all in vitro requirements.