An autoinjector device includes an elongate housing containing a syringe or cartridge having an internal piston for expressing a dose from the syringe or cartridge. A drive mechanism includes a drive member engaging the piston and a drive spring acting on the drive member. A side-operated trigger arrangement includes a retention element movably mounted in the housing from a retaining position in which the drive member is kept in a cocked condition, and a release position in which the drive member may more forwardly under spring pressure. An outer sleeve is mounted on the housing movable between a position in which the retention element is prevented from moving to release the plunger, and a position in which the retention member moves freely. The outer sleeve includes a trigger wall portion which may be depressed to move the retention element once the retention element is free to move, releasing the plunger.
