A drive mechanism for a medication delivery device is presented having a housing, a rotation member that rotates in a first direction with respect to the housing during setting of a dose of a medication and rotates in a second direction with respect to the housing during delivery of the dose, the second direction being opposite to the first direction. The device also has a piston rod that is displaced in a distal direction with respect to the housing for delivering the dose, a drive member which follows rotational movement of the rotation member in the second direction during delivery of the dose, and a stop member which prevents rotational movement of the drive member with respect to the housing in the first direction during setting of the dose.
