Prescription Diet z/d is clinical nutrition specially formulated to help avoid skin and digestive signs from adverse food reactions in cats. It's made in the USA with global ingredients you can trust, and was developed by Hill's nutritionists and veterinarians. This food is formulated to promote an environment that makes it difficult for struvite and calcium oxalate crystals to form. It also has clinically proven antioxidants to help support a healthy immune system. Please consult your veterinarian for further information on how Prescription Diet foods can help your cat continue to enjoy a happy and active life.