Closure apparatus for a drinking container

A closure apparatus is fitted onto a container opening of a drinking container with an inner space for reception of a drinking liquid. The closure apparatus includes a chamber body that defines therein a receiving chamber, the content of which is introducible into the inner space of the drinking container. The closure apparatus further includes a closure element that selectively closes a first opening of the chamber body, and an axially slidably displaceable cover element that selectively closes a second introduction opening of the chamber body. The content of the receiving chamber is releasable into the inner space of the drinking container through the second introduction opening by an axial sliding displacement of the cover element.