The invention relates to a reusable syringe with a syringe body (1) for receiving an ampoule. At the front end of the syringe body (1) there is an opening (11) which defines an axis (27) along which a needle (10) can be inserted. A plurality of holding segments (7, 8, 25) are arranged around this axis (27) and engage behind a needle carrier (9) in the longitudinal direction. According to the invention, a holding segment (7) designed as a thread part is movable in the radial direction. The invention further relates to a system composed of a reusable syringe, a needle carrier, and a container for used needles. Moreover, the invention includes an associated method for connecting and releasing a needle (10) of a reusable syringe. The movable holding segment (7) facilitates the release of the threaded connection of the needle carrier (9) from the syringe body (1) and makes the reusable syringe safer to use.