A resettable drive mechanism comprising a housing, a drive member rotatable in a second direction for delivering a dose of a medication, a piston rod driven by the drive member when it rotates in the second direction. A stop member prevents rotation of the drive member in a first direction opposite to the second direction, when the stop member engages the drive member. A clutch member is movable between a delivery position and a reset position. When the clutch member is in the delivery position, the stop member and the drive member are engaged and the drive member is prevented from rotating in the first direction, and when the clutch member is in the reset position, the drive member and the stop member are disengaged, the drive member is rotatable in the first direction and the piston rod is movable in the proximal direction.
