a syringe body defining a proximal portion and a distal portion, the syringe body having first and second cavities disposed at the proximal portion of the syringe body, the second cavity being larger than the first cavity;

a needle removeably engageable to the body distal portion;

a piston disposed within the body and biasable to the body proximal portion via a vacuum force when the piston is traversed toward the body distal portion, the piston being bi-directionally traverseable within the syringe body between the proximal portion and the distal portion before completion of the injection stroke, the piston being engageable to the needle after completion of the injection stroke;

a shaft attached to the piston and disposed within the body, the shaft defining a first side and an opposed second side, the shaft extending through the proximal portion of the body, traversal of the shaft though the body operative to traverse the piston within the syringe body;

a braking mechanism comprising first and second brake member halves which are disposed in the first cavity of the body, the first brake member half biased toward and frictionally engaged to the first side of the shaft and the second brake member half biased toward and frictionally engaged to the opposed second side of the shaft for providing a braking force substantially equal to the vacuum force to maintain a position of the piston within the syringe body before completion of the injection stroke, the first and second brake member halves completely disengaged from the shaft after completion of the injection stroke by axially traversing the first and second brake member halves into the second cavity so the vacuum force withdraws the needle into the syringe body to prevent accidental needle pricking and needle reuse; and

a ram attached to the shaft for axially driving the first and second brake member halves from the first cavity into the second cavity when the injection stroke is completed.