A powder inhaler for administering powder by inhalation which includes: an inhaler body having an opening therein; an inhalation unit disposed in the inhaler body, the inhalation unit including an inhalation channel through which powder is in use inhaled; a dosing unit for providing a dose of powder to the inhalation channel disposed in the inhaler body so as to be rotatable about the central axis thereof, wherein the dosing unit includes a central shaft which is co-axial with the central axis of the inhaler body and has a spiral groove or protrusion on the end face thereof; and an indicating wheel for providing an indication as to the usage of the inhaler disposed in the inhaler body, the indicating wheel having a toothed periphery for engaging the spiral groove or protrusion on the shaft and being disposed such that at least a part thereof is visible through the opening and so as to be rotatable within a diametrical plane containing the central axis of the inhaler body. One side surface of the indicating wheel includes at least one indication which is representative of the usage of the inhaler. In addition, the inhaler body includes a recess in which the opening is provided. The opening allows at least a part of the one side surface of the indicating wheel to be viewed.