Felimazole®, with the active ingredient methimazole, reduces thyroid hormone synthesis and treats hyperthyroidism in cats. It is contraindicated for pregnant or lactating females, as well as cats with immune-mediated diseases, renal or hepatic conditions, or blood disorders. Side effects include vomiting, loss of appetite, or depression, which are usually temporary. Veterinary monitoring is essential, including regular blood and urine tests. The medication may interact with other treatments. Store it in a dry place, away from children and animals.