Hill's Prescription Diet y/d Dry Cat Food is an easy and convenient way to manage a cat's overactive thyroid and the only clinically proven nutrition to decrease thyroid hormone production in 3 weeks when fed as the sole source of nutrition. It's made in the USA with global ingredients you can trust, and was developed by Hill's nutritionists and veterinarians. This food is also formulated to promote a urinary environment that reduces the risk of developing struvite and calcium oxalate crystals. Please consult your veterinarian for further information on how Prescription Diet foods can help your cat continue to enjoy a happy and active life.