The drive mechanism for a drug delivery device comprises a piston rod, which is displaced in a distal direction for a delivery of a dose and in a proximal direction for a reset, and a rotatable drive member, which is threadedly engaged with the piston rod and rotates during the delivery of the dose. A biasing member is provided, which is loaded by the rotation of the drive member during the delivery of the dose and tends to rotate the piston rod with respect to the drive member in such a way that the piston rod is screwed into the drive member and is thereby advanced in the proximal direction. The drug delivery device is provided with such a drive mechanism.
