Zenidog Collars contain calming canine appeasing pheromone. Long-lasting: Zenidog Collars last up to 3 months, 3 times longer than other pheromone collars. Effective: Zenidog Collars have been shown to reduce stress-related behaviours by 89%. Suitable for dogs and puppies and can be used with an antiparasitic collar. Ideal for everyday use, leave the collar on your dog continuously for 3 months. Available in 2 adjustable sizes - small and medium/large.