An inhaler (1) for the delivery of a dose of powdered medicament for inhalation by a user comprising a housing (2) containing a cylinder (5) defining a chamber (5a) and a piston (6) movably received in the cylinder to enable a user to generate a charge of compressed air in the chamber to entrain a dose when the charge is released, wherein the cylinder and the piston include co-operating means (8, 9) thereon operable to draw the piston into the cylinder to compress a charge of air in the chamber in response to rotation of the piston.
