When a trigger of an injection device is released, a main spring (4) expands, driving a member (7) forwards. This compresses a weak spring (11), but a spring (5) is stiff enough to remain expanded. A syringe (2) is thus thrust forwards via a collar (9), so that a needle (3) projects from a barrel (1). The spring (4) continues to expand after the syringe has reached its forward position, with the spring (11) fully compressed, so that the stem (8) of the member (7) acts on a piston (14) within the syringe (2), to expel the dose while the spring (5) is caused to be compressed. The spring (5) ensures that the syringe is retained in its forward position during this phase.