An inhaler for producing an inhalable aerosol of a powdered medicament comprises a cyclone (1) with a tangential air inlet (3) and an axial air outlet (4). The cyclone (1) aerosolises and retains an aerosol of powdered medicament in an airflow circulating between the inlet (3) and the outlet (4). The cyclone (1) has an exit port (2) which is open to atmosphere. When the aerosol is to be inhaled, the pressure in the cyclone (1) is increased by increasing the airflow to the inlet (3) which causes the aerosol to discharge through the exit port (2). The inhaler has the advantage that the rate of discharge of the aerosol can be controlled independently of the rate of airflow required to aerosolise the medicament.