An injection device (110) comprises a first sub-assembly (210) and a second sub-assembly (310). The first sub-assembly (210) comprises a chamber (224) for holding a fluid. The chamber (224) comprises an inner surface and an exit aperture (226). The first sub-assembly (210) comprises a stopper (222) movably disposed within the chamber (224) and having an outer surface substantially in contact with the inner surface about its perimeter. The first sub-assembly comprises an adapter (214) adapted to transfer fluid into the chamber. The second sub-assembly (310) comprises a releasable drive mechanism, said drive mechanism comprising an elongate shaft which is driven against the stopper upon activation of the drive mechanism
