A closure attachable over the opening of a container that selectively facilitates mixing of a component (e.g., supplement, vitamins, etc.) of any appropriate form (e.g., powders, flakes, liquids) with a liquid in the container to create a mixture. In one aspect, the closure includes a body, a storage compartment within the body, a nozzle movably received on the annular wall, a cap receivable over a portion of the body and the nozzle, an annular pull strip surrounding the body and spacing the first end of the cap from an outer collar of the body, and a plunger disposed within the storage compartment that is adapted to selectively break a seal to allow for mixing between the component and the liquid.