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