Respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are pathological conditions affecting the airways of the respiratory system. Currently more than 90 million people are suffering from respiratory diseases, and COPD is predicted to become the third leading cause of death in the world by 2030. Inhalation devices are commonly used in the treatment of respiratory diseases, where an aerosolised medication is delivered to the lungs of the patient via inhalation. The inspiratory flow rate is one of the main factors affecting the drug deposition in the lung, but is currently not controlled in most inhalation systems. The purpose of this master thesis is to design, manufacture and characterize a passive flow regulator device for portable inhalation systems. The designed prototype utilises the principle of a Venturi nozzle and membrane deflection to create a variable flow constriction, which acts as a negative feedback loop for the flow rate regulation. The flow regulator is based on a previously working device used for controlling exhalation flow rate in the range of 3 L/min. Experimental results are evaluated and compared to an analytical solution of the classical Venturi design. Additionally, membrane deflection is measured to analyse the physical behaviour of the membrane within the device. The flow regulating device is scaled up for inhalation flow rate ranges (>30 L/min) and a flow rate sensor is constructed for the measurements. The passive control of flow rates using a deflecting membrane is deemed promising. However, further improvements of the scaled up model used for inhalation are necessary.