A dispensing cap system for dispensing a supplement material through a bottle neck opening and into the bottle. An exemplary embodiment includes a cap member configured for connection to beverage bottle necks of different sizes. A seal member is arranged to provide a liquid seal against the neck opening. A valve member passes through a storage member attached to the cap member, and is configured for movement between a storage position and a dispensing position, in which passage is permitted of the supplement material from the storage member into the bottle. A nipple member may be positioned over the valve member to allow the bottle contents to be utilized or consumed.