A drive mechanism suitable for the efficient transmission of an actuation force in drug delivery devices, which allows dispensing of large doses of drug and which provides an easy to use correction of a set dose. The drive mechanism comprises a plunger rod (26) having a non-circular cross section and being hollow and being prevented from rotation a lead screw (25) engaged with a plunger rod (26) a dose setting dial (22) rotatably moving towards the proximal end during dose setting and rotatably moving towards the distal end during dose dispensing an inner cylinder (23) being releasable connected to the dose setting dial (22) such that relative rotation between the dose setting dial (22) and the inner cylinder (23) is prevented during dose setting but is allowed during dose dispensing and a plunger rod holder (27) which prevents the plunger rod holder (26) from moving towards the proximal end during dose setting, but allows the plunger rod (26) to move towards the distal end during dose dispensing.
