An autoinjector for being triggered for expelling a single dose of drug from a held cartridge, the autoinjector comprising: - a base (220, 200', 1200, 1204), - a drug cartridge arranged relative to the base (220, 200' 1200, 1204), the cartridge 600) comprising a) an elongated body having a distal end and a proximal end and defining a central longitudinal axis, the body having a distally arranged outlet adapted for connection to a held needle, and b) a piston accommodated in the body, the piston configured for being driven axially in the distal direction to expel a dose of a drug through the outlet, - a plunger (310,400) adapted upon triggering for moving in a distal direction relative to an initial axial position and transferring a force to move the piston, - an actuator providing stored energy, the actuator configured for providing a force to act on the plunger (310,400) to drive the piston distally, - a needle shield (350, 380') axially movable relative to the base (220, 200', 1200, 1204) in a proximal direction from an initial extended position via a triggering position to a trigger release position, wherein a plunger release element (320', 1320) is operatively coupled to the plunger (310, 400) to prevent the plunger (310, 400) from moving distally relative to the plunger release element (320', 1320), wherein the plunger release element (320', 1320) defines a thread (325', 1325) and the base (200', 220, 1200, 1204) associates with a base thread component (204', 1204) that defines a thread adapted for engaging with the thread (325', 1325) of the plunger release element (320', 1320), wherein the needle shield (350, 380') is operatively coupled to the plunger release element (320', 1320) and the base thread component (204', 1204) to define a releasable retaining mechanism configured to, in an initial state where the needle shield (350, 380') assumes its initial extended position, retain the plunger release element (320', 1320) threadedly engaged with the base thread component (204', 1204) in a predefined relative rotational and axial position where the force of the actuator provides bias for urging relative rotation between the plunger release element (320', 1320) and the base thread component (204', 1204) in an expelling rotational direction, and wherein the needle shield (350, 380') is configured for operating the retaining mechanism to release the retaining of the plunger release element (320', 1320) and base thread component (204', 1204) from the predefined relative rotational and axial position upon the needle shield (350, 380') being moved into its trigger release position, characterized in that a first pair of cooperating means (386', 206') operatively couples the needle shield (350, 380) with the base (200', 220) and a second pair of cooperating means (388',328') operatively couples the needle shield (350, 380') with the plunger release element, the first pair of cooperating means (386', 206') and the second pair of cooperating means (388',328') being configured to induce relative rotation between the plunger release element and the base thread component as the needle shield (350,380') moves from the initial extended position towards the triggering position so that energy stored in the actuator changes as the needle shield (350, 380', 1380) moves from the initial extended position towards the triggering position. - a base (220, 200', 1200, 1204), - a drug cartridge arranged relative to the base (220, 200' 1200, 1204), the cartridge 600) comprising a) an elongated body having a distal end and a proximal end and defining a central longitudinal axis, the body having a distally arranged outlet adapted for connection to a held needle, and b) a piston accommodated in the body, the piston configured for being driven axially in the distal direction to expel a dose of a drug through the outlet, - a plunger (310,400) adapted upon triggering for moving in a distal direction relative to an initial axial position and transferring a force to move the piston, - an actuator providing stored energy, the actuator configured for providing a force to act on the plunger (310,400) to drive the piston distally, - a needle shield (350, 380') axially movable relative to the base (220, 200', 1200, 1204) in a proximal direction from an initial extended position via a triggering position to a trigger release position,