Catheter cannula, catheter, and catheterization method, for administering a fluid or/and substance to, or for draining a fluid or/and substance from, a treatment space of a body vessel, duct, or cavity. In some embodiments the cannula includes: an elongated flexible tube mountable on a needle, and having an invasive section and a non-invasive section； and at least one anchoring element protruding from, a surface of the invasive section in a manner such that an operative configuration of each anchoring element increases outer circumferential diameter of the cannula to an extent less than lumen diameter of the body vessel, duct, or cavity, at the treatment space, thereby anchoring the invasive section to inside the body vessel, duct, or cavity, at the treatment space. The catheter includes a needle and the cannula mounted thereupon.
