A nasal delivery device (10,210,310) comprising: an air-receiving section (12,212) that has a first passageway therethrough to allow air to pass through the air-receiving section (12,212); a powder reservoir (18,218); a powder-reservoir receiving section (14,214) sized to receive the powder reservoir (18,218); and a powder-delivery section (16,216) that has a second passageway therethrough to allow aerosolized powder from the powder reservoir (18,218) to pass through the powder-delivery section (16,216), wherein the first passageway has a first end and a second end, the first end being further from the powder-reservoir receiving section (4,214) and the second end being at or near the powder-reservoir receiving area (14,214), wherein the second end of the air-receiving section (12,212) comprises a flattened region (52,252) so that air exiting the air-receiving section (12,212) has a generally flattened profile; and wherein the powder reservoir (18,218) contains a treatment agent and an excipient, the powder reservoir (18,218) comprising a pair of opposing sidewalls, the opposing side walls being generally curved toward one another to facilitate air flow across an inside surface of each sidewall, so that in use the powder reservoir (18,218) is narrower at the bottom than at the top, the device (10,210,310) further comprising: a sealing member for sealing the treatment agent and the excipient inside the powder reservoir (18,218); and an attachment member extending from the powder reservoir (18,218) to facilitate coupling of the powder reservoir (18,218) to the powder-reservoir receiving section (14,214) of the device (10,210,310). an air-receiving section (12,212) that has a first passageway therethrough to allow air to pass through the air-receiving section (12,212); a powder reservoir (18,218); a powder-reservoir receiving section (14,214) sized to receive the powder reservoir (18,218); and a powder-delivery section (16,216) that has a second passageway therethrough to allow aerosolized powder from the powder reservoir (18,218) to pass through the powder-delivery section (16,216), wherein the first passageway has a first end and a second end, the first end being further from the powder-reservoir receiving section (4,214) and the second end being at or near the powder-reservoir receiving area (14,214), wherein the second end of the air-receiving section (12,212) comprises a flattened region (52,252) so that air exiting the air-receiving section (12,212) has a generally flattened profile; and wherein the powder reservoir (18,218) contains a treatment agent and an excipient, the powder reservoir (18,218) comprising a pair of opposing sidewalls, the opposing side walls being generally curved toward one another to facilitate air flow across an inside surface of each sidewall, so that in use the powder reservoir (18,218) is narrower at the bottom than at the top, the device (10,210,310) further comprising: a sealing member for sealing the treatment agent and the excipient inside the powder reservoir (18,218); and an attachment member extending from the powder reservoir (18,218) to facilitate coupling of the powder reservoir (18,218) to the powder-reservoir receiving section (14,214) of the device (10,210,310). a sealing member for sealing the treatment agent and the excipient inside the powder reservoir (18,218); and an attachment member extending from the powder reservoir (18,218) to facilitate coupling of the powder reservoir (18,218) to the powder-reservoir receiving section (14,214) of the device (10,210,310).