The fillable closure is used to trigger the emptying of a capsule that can be inserted in the closure and filled separately. The closure consists of a closing cap which can be attached to the neck of a container and in which a separately fillable capsule can be inserted in the closed state from beneath. The region above the inserted capsule on the closing cap forms a push button. A downwardly projecting protuberance is molded on the lower face. The protuberance abuts against the inserted capsule. Using pressure from above, the push button can be pressed to deform an initially convex shape as seen from above into a concave shape, the protuberance pushing the upper face of the capsule and the content thereof downward. A film, which forms the lower face of the capsule, is thus placed under tensile stress such that it breaks or bursts along weakened lines.