Hyperthyroidism is the most common endocrine disorder in older cats, causing significant welfare impacts from weight loss, heart disease, and anxiety — but it is highly treatable when diagnosed early.
Undiagnosed and untreated hyperthyroidism causes sustained welfare harm. Cats feel constantly hungry but lose weight, experience gastrointestinal upset, and suffer cardiovascular strain. The elevated metabolism causes a state similar to chronic anxiety — restlessness, irritability, and inability to settle. Heart changes can cause painful cardiac events. High blood pressure secondary to hyperthyroidism damages eyes (retinal detachment causing blindness) and kidneys. The welfare impact of untreated hyperthyroidism in an older cat over months or years is substantial. Conversely, treatment typically produces dramatic welfare improvements: cats return to normal weight, become calmer, and live significantly longer. Regular veterinary screening for older cats is the key intervention.