Drive mechanism for an injection device, the mechanism comprising: - a housing (4, 5; 104, 105), - a dial member (6; 106), - a torsion spring (12; 112) fixed between the housing (4, 5; 104, 105) and the dial member (6; 106) such that energy is accumulated in the torsion spring (12; 112) upon rotation of the dial member (6; 106) relative to the housing (4, 5; 104, 105), - a drive member (8; 108) engaging a lead screw (9; 109), - a first clutch (18; 118) rotationally coupling the drive member (8; 108) and the housing (4, 5; 104, 105) in a coupled state and allowing relative rotation between the drive member (8; 108) and the housing (4, 5; 104, 105) in a de-coupled state, - a second clutch (19; 119) rotationally coupling the drive member (8; 108) and the dial member (6; 106) in a coupled state and allowing relative clockwise and anti-clockwise rotation between the drive member (8; 108) and the dial member (6; 106) in a de-coupled state, wherein the second clutch (19; 119) comprises a ratchet clicker with teeth (19a, 19b; 119a, 119b) having in the clockwise and the anti-clockwise direction differently ramped tooth angles such that the teeth (19a, 19b; 119a, 119b) are allowed to override each other in the de-coupled state of the second clutch (19; 119) with a different resistance in the clockwise and the anti-clockwise direction, wherein the drive mechanism further comprises a nut (11; 111) which is guided axially displaceable and non-rotatable on the drive member (8; 108) and which has an external thread engaging an internal thread of the dial member (6; 106) such that relative rotation between the drive member (8; 108) and the dial member (6; 106) during dose setting causes the nut (11; 111) to move towards an end stop, wherein the nut (11; 111) prevents setting of a dose exceeding the amount of a medicament in the injection device, wherein during dose setting and dose resetting the first clutch (18; 118) is in its coupled state and the second clutch (19; 119) is in its de-coupled state, wherein during dose dispensing the first clutch (18; 118) is in its de-coupled state and the second clutch (19; 119) is in its coupled state, characterized in that the first clutch (18; 118) is coupled and de-coupled by axially displacing the drive member (8; 108) relative to the housing (4, 5; 104, 105) or, alternatively, by axially displacing a trigger clutch relative to the drive member (8; 108), wherein the drive mechanism further comprises a trigger pivotably attached to the housing (4, 5; 104, 105), wherein the trigger engages the trigger clutch such that swiveling of the trigger relative to the housing (4, 5; 104, 105) axially displaces the trigger clutch. - a housing (4, 5; 104, 105), - a dial member (6; 106), - a torsion spring (12; 112) fixed between the housing (4, 5; 104, 105) and the dial member (6; 106) such that energy is accumulated in the torsion spring (12; 112) upon rotation of the dial member (6; 106) relative to the housing (4, 5; 104, 105), - a drive member (8; 108) engaging a lead screw (9; 109), - a first clutch (18; 118) rotationally coupling the drive member (8; 108) and the housing (4, 5; 104, 105) in a coupled state and allowing relative rotation between the drive member (8; 108) and the housing (4, 5; 104, 105) in a de-coupled state, - a second clutch (19; 119) rotationally coupling the drive member (8; 108) and the dial member (6; 106) in a coupled state and allowing relative clockwise and anti-clockwise rotation between the drive member (8; 108) and the dial member (6; 106) in a de-coupled state,