An injection device has a plunger which retracts from a cartridge bung between doses in order not to promote leakage. The device is preferably a torsion spring injector having a main housing 504, a plunger 8, a drive gear 7 and a release trigger 506. The plunger comprises a leadscrew 9 with a cap 11 which engages the bung (12, figure 2). Rotation of the drive gear around the leadscrew drives the plunger axially towards the bung. The release trigger has a locking ring 520 with axially extending teeth 521 for engaging with corresponding teeth 519 on the drive gear. The teeth may be curved (figures 3BÂ-3D), or have beveled ends (figure 4A), or the trigger may slide in a doglegged slot 522, such that movement of the release trigger into its rest position causes counter-rotation of the drive gear so as to retract the plunger away from the bung.
