An operable single-use syringe includes a barrel having an inside surface defining a chamber for retaining fluid and an open proximal end. A plunger rod having an elongate body portion and a stopper at its distal end slidably positioned in fluid-tight engagement in the barrel. A locking element is positioned in the barrel between the plunger rod and the inside surface of the barrel. The locking element has a base and two leg members projecting therefrom that are positioned in longitudinal grooves in the plunger rod. The locking element only moves distally in the barrel and prevents re-use of the syringe after its contents have been discharged.
