Abstract: Handheld motor-driven drug reconstitution and auto-injector device (1) having a proximal drive system (2) comprising an elongated body (3) housing a controllable drive motor (6), and an axially drivable piston rod (7), and a distal drug cartridge holder assembly (11) housing a multiple chamber (30, 31) drug cartridge (25), the cartridge holder assembly (11) being releasably attached to a distal zone (23) of the drive system (2), the drive system (2) and cartridge holder assembly (11) being configured to impart a movement to the drug cartridge holder assembly (11) in which said drug cartridge holder assembly (11) is moved from a first substantially extended distal configuration along the central longitudinal axis, to a second substantially collapsed proximal configuration along the central longitudinal axis, the relative movement of the drug cartridge holder assembly (11) effecting reconstitution of an injectable product from substances contained in each of the chambers (30, 31).