Abstract: An injection device delivers a preselected dose of a drug, such as insulin, from a conventional syringe. The device includes a sleeve having a first opening and a cavity sufficiently large to house a barrel of a conventional syringe. The sleeve further includes a second opening through which a cannula of the syringe extends and which is sufficiently small to retain the barrel of the syringe. A plunger-engaging cap is positioned within the sleeve in sliding relationship and engages a plunger of the syringe. The sleeve includes a slot preferably extending longitudinally along the sleeve and the plunger-engaging cap includes a pin extending outwardly from the cap's surface and positioned within the slot.