A drive mechanism (3) for a medication delivery device is disclosed. The drive mechanism comprises a housing (17) and a rotation member (34) adapted to be rotated in a first direction during setting of a medication dose and to be rotated in a second direction during delivery of the dose. A drive member (20) follows rotation the rotation member in the second dose delivery direction and a stop member (26) prevents rotation of the drive member (20) in the first direction when setting the dose. A piston rod (12) is adapted to be displaced in a distal direction by rotation of the drive member (20) in the second direction which is converted into rotation of the piston rod (12).
