A breath-actuated dry powder inhaler, comprising: (a) a body; (b) a dose-ring subassembly comprising a dose ring and an airway including a swirl chamber and a mouthpiece , wherein the airway has airway inlets and an airway outlet , said airway forming a conduit for bypass air and drug laden air to mix and enter the swirl chamber, and wherein the dose ring is fully enclosed in the body of the dry powder inhaler during use and is capable of rotating through a segment of the airway, said dose ring comprising a plurality of sealed foil pockets , with each pocket containing dry powder comprising a dose of a drug, (c) a mouthpiece cover rotatable between a substantially closed and a substantially open position (d) a breath actuated mechanism (BAM) comprising a BAM flap movable from a substantially closed position to a substantially open position and a bistable biasing spring holding the BAM flap in the substantially closed position, the BAM being primed by rotation of the mouthpiece cover from the substantially closed to the substantially open position such that breath induced low pressure can overcome the bistable biasing spring to allow opening of the BAM flap wherein the bistable spring acts to move the BAM flap to the open position, and (e) a piercer blade ; and (f) a dose opening mechanism configured to be energized by the opening of the mouthpiece cover and being held in a latched position until disengaged by movement of the BAM flap; wherein during the BAM flap travel from the closed to the open position, the movement of the BAM flap forces a latch retaining the energized dose opening mechanism to be disengaged, thereby triggering dose opening by the piercer blade, characterised in that the piercer blade is a blade with tangs and is configured to cut a slit in the sealed foil pocket located on the dose ring such that the piercer blade moves through a lower foil, the dose pocket and an upper foil and the tangs fold the foil into flaps which are pushed upwards and towards a long side of the dose pocket as the piercer moves upwards. (a) a body; (b) a dose-ring subassembly comprising a dose ring and an airway including a swirl chamber and a mouthpiece , wherein the airway has airway inlets and an airway outlet , said airway forming a conduit for bypass air and drug laden air to mix and enter the swirl chamber, and wherein the dose ring is fully enclosed in the body of the dry powder inhaler during use and is capable of rotating through a segment of the airway, said dose ring comprising a plurality of sealed foil pockets , with each pocket containing dry powder comprising a dose of a drug, (c) a mouthpiece cover rotatable between a substantially closed and a substantially open position (d) a breath actuated mechanism (BAM) comprising a BAM flap movable from a substantially closed position to a substantially open position and a bistable biasing spring holding the BAM flap in the substantially closed position, the BAM being primed by rotation of the mouthpiece cover from the substantially closed to the substantially open position such that breath induced low pressure can overcome the bistable biasing spring to allow opening of the BAM flap wherein the bistable spring acts to move the BAM flap to the open position, and (e) a piercer blade ; and (f) a dose opening mechanism configured to be energized by the opening of the mouthpiece cover and being held in a latched position until disengaged by movement of the BAM flap; <EOS>