Modified medical syringe with a flow regulator for the administration of anaesthesia, which allows for anaesthesiologists to handle the needle, control continuous aspiration and administer the anaesthetic with a single hand, thereby preventing intravascular injections. It comprises a flexible tube, designed to be introduced inside the barrel, which supplies the anaesthetic; a cylindrical body located on the rod, equipped with a protuberance along a semicircle located on the proximal side of the body and a through-hole wherein one end of the flexible tube may be introduced; a cylindrical cap located inside the syringe barrel, equipped with a longitudinal groove along its cylindrical side, which is designed to house the aforementioned flexible tube; a preloaded spring around the rod located between the cap and the support disk; and a pressurization device connected to the flexible tube.