A syringe for medical applications includes a syringe body having an inner wall, a first stop, located along the inner wall, to leave at least one first blank surface on the inner wall and a plunger sliding along the inner wall of along a longitudinal axis of the syringe, the plunger including a plunger head and an operating rod, connected to the plunger head, including, on its outer surface, at least one first rack arranged longitudinally along the operating rod, the first rack including protruding teeth. The first stop and the protruding teeth are also shaped and constituted so as to prevent the plunger from lowering again due to pressure on the operating rod, unless the first rack is disengaged by rotating the plunger within the syringe body around the longitudinal axis so that the first rack faces the first blank surface of the inner wall of the syringe body.
