The FELIWAY® Friends Refill is designed for using with the FELIWAY® Friends Diffuser. Each 48ml Refill vial lasts for 4 weeks. FELIWAY® Friends contains a man-made copy of the cat appeasing pheromone that a mother cat naturally releases to her kittens after birth. This pheromone helps the kittens feel safe and secure and promotes bonding. The pheromone has been clinically proven to have the same effect on adult cats FELIWAY® Friends Diffuser aids in reducing tension and conflict between multiple cats to help them live in harmony together within the same household.