These refills are for use with FELIWAY Optimum diffusers, and it calms cats better than ever and in more situations. It contains the patented latest generation of Feline Pheromone Complex, developed by the FELIWAY research team. This new pheromone discovery represents the next generation with improved efficacy, delivering advanced calming messages, helping your cats feel comfortable and secure at home. FELIWAY Optimum is clinically proven to help cats with the management of more signs of stress, such as urine spraying, vertical scratching, excessive hiding, and inter-cat conflicts.