Replace your FELIWAY® Optimum Refill every 30 days to continue to create a loving and comfortable home for your cat. FELIWAY® Optimum is the best FELIWAY answer to reduce signs of stress such as: Scratching Urine spraying Tension & conflict between cats Hiding Reactions to changes   FELIWAY® Optimum Refill requires a FELIWAY® Diffuser (diffuser not included) and should be plugged in continuously.  Screw the vial into the diffuser head and plug it into an outlet with the vents up.   Please note: an additional discount code cannot be applied to a subscription