A breath-actuated delivery device includes a mouthpiece through which a subject in use exhales, an air channel which is in fluid communication with the mouthpiece, and a flexible diaphragm which is disposed in the air channel. The diaphragm provides for at least a restricted air flow through the air channel until a predeterminable actuation pressure is developed in the mouthpiece, and, on generation of the predeterminable actuation pressure in the mouthpiece, provides for an air flow through the air channel.