The invention provides an apparatus for use in aerosolized delivery of a powder, and comprises a first chamber containing gas at a first pressure higher than atmospheric pressure, and a second chamber containing gas at a second pressure higher than atmospheric pressure. The apparatus also comprises a powder, contained within the first or second chamber. The first chamber has a first external wall and a separating wall, the separating wall being shared with the second chamber. The first external wall or the separating wall is configured to rupture if the pressure difference across it becomes equal to or greater than a threshold pressure difference. In particular, the apparatus is configured so that the difference between the second pressure and atmospheric pressure is greater than the threshold pressure difference. In an initial state, the apparatus is configured such that the difference between the second pressure and the first pressure is less than the pressure difference required to rupture the separating wall, and the difference between the first pressure and atmospheric pressure is less than the pressure difference required to rupture the first external wall.
