A drug delivery device (100) includes a body (102, 116) having a reservoir (160) disposed therein for containing a medicament and an injection needle (152) for penetrating the skin of a patient, the needle (152) providing a path for the medicament between the reservoir (160) and the patient. The device (100) also includes a plunger (144) movable within the body (102, 116) for causing the medicament to be expelled from the reservoir (160), and a biasing means (140) for biasing the plunger (144) toward the reservoir (160), wherein in a pre-activated position, the biasing means (140) telescopes within itself, and upon activation, provides a force to the plunger (144) for expelling the medicament from the reservoir (160). The biasing means (140) is preferably provided in the form of a conical spring having a variable pitch.
