Abstract: Safety insert for disposable syringes, comprising at least one attachment member whose point allows advance of the stem during injection of the syringe content and prevents its retraction once said injection is performed on attaching to the inner walls of the cylinder, and having at least one perforating member with a gaff at its end able to dig into the plunger and pass through its wall, thus breaking the tightness of the compartment of the cylinder intended to contain the substance to be injected when retraction of the stem is attempted following the injection.