A nasal cannula includes a distribution conduit running along a virtual distribution path. The distribution path defines a longitudinal direction and has two branch openings. A respective supply conduit branches off from each branch opening. The distribution conduit also has two coupling openings arranged spaced apart from the branch openings. The nasal cannula has a plug via which one of the two coupling openings can be sealed as a closure opening. Another of the two coupling openings is designed as a supply opening. The plug has a flow-directing configuration with an exposed flow-directing surface. In a reference state in which the plug is closing the closure opening, the flow-directing surface is arranged in the distribution conduit in the longitudinal extension region of at least one branch opening and positioned relative to the distribution path to deflect treatment gas flowing in the distribution conduit from the supply opening along the distribution path towards at least one of the branch openings.