Comfort Zone Calming Pheromone Diffuser Refill for Cats pairs with all Comfort Zone cat calming diffusers (sold separately). Each refill provides up to 30 days of continuous calming benefits. The drug-free formula mimics a kitty’s natural pheromones to let them know the area is safe and familiar, which helps reduce unwanted behaviors like scratching and urine marking. When used consistently, most cats showed improved behavior after one week. Replace each month for a continuous cat stress relief.