Attachment for a standard syringe and injection device for needle-free injection

Adapter (10) for a standard syringe device (70) for needleless injection of a fluid, with a nozzle adapter (12) and a piston unit (40), wherein the nozzle adapter (12) comprises a skin contact surface (16) arranged at its distal end (14) with an outlet opening (18), a first cylinder section (20) proximally joined to the outlet opening (18) and a second cylinder section (26) joined to the first cylinder section (20), and the piston unit (40) is displaceably supported in the first cylinder section (20) for forming a piston-cylinder unit, and the adapter (10) comprises a fluid line (48) for transporting fluid from the standard syringe device (70) to the outlet opening (18), wherein the piston unit (40) comprises a piston (42) arranged in the first cylinder section (20) and a proximal connection part (44) mechanically connected with the piston (42), with the proximal end of the connection part (44) designed for mechanical connection of a standard syringe device (70) receiving or capable to receive the fluid, so that a force effect from the standard syringe device (70) on the connection part (44) can be realized for displacing the piston unit (40) and expelling a fluid from or drawing a fluid in from the first cylinder section (20).