ThunderEase Calming Collars use a synthetic copy of the natural canine appeasing pheromone that has been proven to help support dogs in a range of stressful situations. It is odorless, non-sedative, non-systemic and can be used alongside all other types of medication. The dog’s body temperature warms the collar and encourages the diffusion of the pheromones. In addition to the decreased amount of stressful situations, the collar is ideal for puppy socialization, travel, kennels and training. Each collar lasts up to 4 weeks. Size: Medium/Large dogs (Fits necks up to 24 inches).