A single-use injector comprising a housing (200) accommodating a mechanical spring energy reservoir (50), a cylinder/piston unit (100), a piston-actuating ram (60) and a trigger unit (80), the spring-locked piston-actuating ram (60) being supported on the housing via support rods, draw hooks or elastic flexural beams. The housing of the injector consists of a thin-walled sheet metal part. Said sheet metal part supports the pretensioned spring energy reservoir and the cylinder/piston unit. The piston (111) of the cylinder/piston unit can be manually displaced by means of a pump rod (140). The single-use injector is compact and has few components, is easy to handle and allows secure storage and functioning. The cylinder/piston unit can be filled when mounted.
