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. For best results, consistent and exclusive long-term feeding of this product is critical for efficacy of the product's benefits. This dry food has a great chicken flavor your cat will love. Dry and canned formulas can be mixed or fed concurrently.