Methods, systems, and devices are described for setting a dose of medicine and injecting the medicine. In one aspect, a method to dispense a medicine includes inserting a cartridge containing a medicine into a cartridge holder coupled to a housing of a medicine injection device, positioning a spine component of the device to make contact with the cartridge in the cartridge holder, selecting a dose of the medicine for injection, in which the selecting includes rotating an injection component of the device to a setting corresponding to the selected dose, and linearly advancing the injection component to rotate a drive gear coupled to the injection component to drive the spine component so as to push the end of the cartridge to dispense the medicine in the amount of the selected dose.