An inhalation simulation system is provided for use with inhalers in particular breath-powered dry powder inhalers. The simulation system can recreate a patient's inhalation profile obtained with an inhaler adapted with a sensing and monitoring device for the detection of characteristic signals generated from the inhaler in use, which signals are transmitted to a computer with an algorithm which is configured to analyze the signals and generate new signals via a transmitter to actuate the inhalation simulation system component parts so that a subject's inhalation profile is replicated simultaneously or in real-time, or stored for later use. Methods of measuring the performance of inhalers are also provided.