A mist inhaler device (200) for generating a mist for inhalation by a user comprises a mist generator device (201) and a driver device (202). The driver device (202) is configured to drive the mist generator device (201) at an optimum frequency to maximise the efficiency of mist generation by the mist generator device (201). A liquid drug such as nicotine, a protein solution, or a medical suspension is transformed into mist by sonification using an ultrasonic transducer 215 which has a planar atomisation surface parallel to the longitudinal length of the mist generator housing. A capillary element 222 extends between a liquid chamber and the sonification chamber, and is retained by the transducer holder (210) such that a part of the capillary element is superimposed on the atomisation surface of the ultrasonic transducer.