Abstract: A method for designing and/or customizing the treatment or for treating by inhalation of a patient suffering from a respiratory or non-respiratory disease including the steps of presenting a patient suffering from the disease; determining the kind of disease of the patient; prescribing at least one drug and/or gas and at least one kind of device to be used for administrating the drug or gas; inputting into a processing element, data chosen among the drug and/or prescribed gas and drug particle size obtained with the prescribed device; inputting into the processing element at least one patient characteristics of the patient; inputting into processing element at least one morphology and/or ventilatory condition of the patient; running a code in the processing element using the input data and conditions thereby calculating a flow and/or deposition characteristics customized to the patient.