A dosing mechanism (6) for delivering a plurality of single metered doses includes a dose delivery mechanism and a non-return mechanism (10), arranged to prevent the dose delivery mechanism from returning toward a primed position until a full metered dose has been delivered. The non-return mechanism includes a track defining an actuation path and a return path and an engagement member arranged to be received within the track. The track and engagement member are relatively moveable such that the engagement member is arranged to move along the actuation path during actuation of the dose delivery mechanism and along the return path during priming of the dose delivery mechanism. At least a portion of the actuation path is provided with a toothed profile to prevent reverse movement of the engagement member in the actuation path.
