An inhaler for producing an inhalable aerosol of powdered medicament is disclosed. The inhaler includes an aerosolising device having a chamber of substantially circular cross-section, inlet and outlet ports at opposite ends of the chamber for the flow of drug laden air through the chamber between said ports and, a bypass air inlet for the flow of clean air into the chamber. The bypass air inlet is configured so that air entering the chamber through said inlet forms a cyclone in the chamber that interacts with the drug laden air flowing between the inlet and outlet ports.
