Disclosed is a method for manufacturing a cannula unit (1) with a cannula housing and a cannula, comprising the steps:- injection molding of a cannula (3) onto a molding core pin with outer diameter d1, wherein the cannula has a distal end (32) with an outer diameter that is larger than the outer diameter of the remaining cannula, a first distal section adjoining the distal end, a second proximal section adjoining the first distal section, and a proximal end；- injection molding of a cannula housing (2) onto the distal end and the first distal section of the cannula；- removing the molding core pin from the cannula； and- threading a piercing needle (5) with outer diameter d4 into the cannula,wherein the diameter d4 of the piercing needle is chosen such that it is smaller than the diameter d1 of the molding core pin.
