Abstract: A cap made up of a body defining an interior volume for receiving a liquid or powdered or pasty composition intended to be transferred into a container having a threaded neck, the cap having a skirt provided with a thread matching the thread of the neck of the container, and a membrane connected to the inner wall of the body by a generally annular peripheral zone, wherein it has a break-off line situated between the peripheral zone and the membrane, such annular peripheral zone being so configured as to bear on the upper surface of the neck of the bottle during screwing of the skirt onto the threaded neck of the container and to cause at least a partial rupture of the break-off line.