An injection device, comprising: a plastic syringe comprising a proximal end, a distal end, and a plunger extending from the proximal end, the syringe comprising a body having a hollow cylindrical interior for receiving medicine and the plunger, and a gripping member on the proximal end, a plastic guard slidably attached to the syringe and having a proximal end and a distal end, the guard being biasable from a first position wherein the distal end of the syringe is exposed toward a second position wherein the guard covers the distal end of the syringe, the syringe and guard having cooperating detents for retaining the guard in the first position and in the second position, first cooperating detents on the syringe and the guard for retaining the guard in the first position, the first cooperating detents comprising a ledge on the proximal end of the syringe and a catch on a latch member extending from the guard and engaging the ledge, as the plunger is advanced within the syringe, the plunger engages the latch member and releases the first cooperating detents whereupon the guard slides toward the second position, and second cooperating detents on the syringe and the guard for retaining the guard in the second position, the second cooperating detents comprising a detent pocket on the guard, a tab on the syringe, characterized by a window extending along the guard and a stop tab on the syringe for engaging the window extending along the guard for limiting proximal motion of the guard when in the first position and distal movement of the guard when in the second position, wherein the tab and the stop tab are configured to travel within the window as the guard moves from the first position to the second position, and wherein the detent pocket is formed in the proximal end of the guard separated from the window, wherein the stop tab and a proximal edge of the window prevent the guard from advancing distally beyond the second position. a plastic syringe comprising a proximal end, a distal end, and a plunger extending from the proximal end, the syringe comprising a body having a hollow cylindrical interior for receiving medicine and the plunger, and a gripping member on the proximal end, a plastic guard slidably attached to the syringe and having a proximal end and a distal end, the guard being biasable from a first position wherein the distal end of the syringe is exposed toward a second position wherein the guard covers the distal end of the syringe, the syringe and guard having cooperating detents for retaining the guard in the first position and in the second position, first cooperating detents on the syringe and the guard for retaining the guard in the first position, the first cooperating detents comprising a ledge on the proximal end of the syringe and a catch on a latch member extending from the guard and engaging the ledge, as the plunger is advanced within the syringe, the plunger engages the latch member and releases the first cooperating detents whereupon the guard slides toward the second position, and second cooperating detents on the syringe and the guard for retaining the guard in the second position, the second cooperating detents comprising a detent pocket on the guard, a tab on the syringe, characterized by a window extending along the guard and a stop tab on the syringe for engaging the window extending along the guard for limiting proximal motion of the guard when in the first position and distal movement of the guard when in the second position, wherein the tab and the stop tab are configured to travel within the window as the guard moves from the first position to the second position, and wherein the detent pocket is formed in the proximal end of the guard separated from the window, wherein the stop tab and a proximal edge of the window prevent the guard from advancing distally beyond the second position.