A method for preparing a solution from a solvent and an active substance in and on a disposable injector with a housing, with an at least intermittently fillable cylinder/piston unit which is arranged thereon and has a manually movable piston, and with a detachable container adapter mounted upstream of the cylinder/piston unit, wherein the container adapter supports a container which can be filled at least temporarily with active substance and which is closable by an openable stopper.
