Felimazole 2.5 mg Tablets for Cats Antithyroid agent Methimazole is given to lower thyroid hormone levels. It is important to understand that methimazole does not cure an overactive thyroid but controls the disease if given to the animal for the rest of its life. Veterinarians may also prescribe methimazole for dogs to protect their kidneys while they are receiving cisplatin chemotherapy. The FDA (U.S. Food & Drug Administration) has approved this drug for treating hyperthyroidism in cats. The FDA allows veterinarians to prescribe and use products containing this drug in other animal species in certain situations. You and your veterinarian can discuss why this drug is the most appropriate choice.