A brush, in particular a toothbrush, including a head part with a cleaning structure with bristles, a handle part and a neck part, a cavity with at least one outlet opening for an active substance being located in the head or neck part. In one embodiment, the cavity incorporates an active substance element, which contains the active substance in a carrier material and releases the substance in a controlled manner when it comes into contact with water. The cavity may be adapted to the shape of an active substance element by means of defined external contours. The volume of the cavity is preferably 1-2 times and no more than 4 times greater than the volume of the active substance element, ensuring that the latter is preferably surrounded by water during use. This allows the active substance to be effectively metered and ensures the brush is easy to use.