A drive mechanism for a drug delivery device, comprising: - a housing (13, 17), - a piston rod arranged inside the housing (13, 17), - a drive member arranged inside the housing (13, 17), the drive member being rotatable with respect to the housing (13, 17), - a rotation member rotatable with respect to the housing (13, 17), - a dose member, which is movable between a first axial position with respect to the housing (13, 17) and a second axial position that is axially spaced from the first axial position, - an engagement of the dose member with the housing (13, 17), the engagement allowing the dose member to move according to a set/deliver path between the first axial position and the second axial position in either direction or to move according to a cancel path from the second axial position to the first axial position, and - an engagement of the dose member with the rotation member and a unidirectional rotational engagement of the rotation member with the drive member by a clutch in such a manner that the rotation member is rotated when the dose member is moved according to the set/deliver path and the drive member is not rotated when the dose member is moved according to the cancel path, characterized in that - the piston rod comprises a thread engaged with the housing (13,17), so that a rotational movement of the piston rod is converted into a movement of the piston rod with respect to the housing (13, 17) in a distal direction, - the piston rod comprises a track engaged with the drive member, so that an axial movement of the piston rod relative to the drive member is allowed and a rotational movement of the drive member with respect to the housing (13, 17) is converted into a rotational movement of the piston rod with respect to the housing (13, 17), and - the dose member is threadedly engaged with the rotation member. - a housing (13, 17), - a piston rod arranged inside the housing (13, 17), - a drive member arranged inside the housing (13, 17), the drive member being rotatable with respect to the housing (13, 17), - a rotation member rotatable with respect to the housing (13, 17), - a dose member, which is movable between a first axial position with respect to the housing (13, 17) and a second axial position that is axially spaced from the first axial position, - an engagement of the dose member with the housing (13, 17), the engagement allowing the dose member to move according to a set/deliver path between the first axial position and the second axial position in either direction or to move according to a cancel path from the second axial position to the first axial position, and - an engagement of the dose member with the rotation member and a unidirectional rotational engagement of the rotation member with the drive member by a clutch in such a manner that the rotation member is rotated when the dose member is moved according to the set/deliver path and the drive member is not rotated when the dose member is moved according to the cancel path, - the piston rod comprises a thread engaged with the housing (13,17), so that a rotational movement of the piston rod is converted into a movement of the piston rod with respect to the housing (13, 17) in a distal direction, - the piston rod comprises a track engaged with the drive member, so that an axial movement of the piston rod relative to the drive member is allowed and a rotational movement of the drive member with respect to the housing (13, 17) is converted into a rotational movement of the piston rod with respect to the housing (13, 17), and - the dose member is threadedly engaged with the rotation member.