A pen-type injector for receiving a medication containing member. The injector comprises a housing 1 and a torsion spring 4 contained within the housing and coupled to a drive member 8. A dose setting knob 2 is coupled to the spring 4, and rotatably coupled to the housing 1 such that rotation of the knob relative to the housing in a first direction results in compression or twisting of the spring. A user actuable trigger 12 is provided for releasing the spring 4 to push the drive member 8 through the housing 1. A user actuable button 6 is coupled to the housing 1 for axial motion relative thereto, said button 6 being coupled to the torsion spring 4 to cause the spring to unwind or expand in discrete steps with each press of the button.