Valved holding chamber for use with dry powder inhaler

A valved holding chamber comprising:

• a holding chamber adapted to contain a substance and comprising an input end adapted to receive a dry powder inhaler, an output end and an expandable interior volume defined between the input end and output end;
• an inhalation valve disposed at the output end of the holding chamber and moveable to an open position in response to an inhalation flow through the interior volume;
• and
• an expander coupled to the holding chamber, wherein the expander is moveable from a first configuration, wherein the expandable interior volume comprises a first interior volume, and a second configuration, wherein the expandable interior volume comprises a second interior volume, wherein the second interior volume is greater than the first interior volume.