Helps to RELAX and CALM dogs when difficult and challenging situations arise Zylkene® Capsules contain casein, a naturally derived ingredient extracted from milk protein that is clinically proven to calm and relax animals. Palatable and easy to give, the capsules are administered to dogs and cats to help them cope with difficult and challenging situations such as a change in environment, moving to a new home, vet visit, the arrival of a new baby or animal, weaning, traveling, fireworks or whenever the pet’s routine is altered.