The drive mechanism comprises a drive member inside a housing, a rotation member and a dose member. The drive member is rotatable with respect to the housing. The rotation member is also rotatable and unidirectionally rotationally engaged with the drive member. The dose member is able to move along a set/deliver path between a first axial position and a second axial position in either direction or to move along a cancel path from the second axial position to the first axial position. An engagement of the dose member with the rotation member causes the rotation member to rotate when the dose member is moved along the set/deliver path. The drive member is not rotated when the dose member is moved along the cancel path. A button in/out spline can be provided for the set/deliver path and a cancel spline for the cancel path.