Hyperthyroidism in Cats & Not Eating

A rare form of hyperthyroidism makes your cat lose his appetite.
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Hyperthyriodism occurs when your cat's thyroid gland becomes a little overzealous and kicks out too much thyroid hormone into Mr. Fuzzypants' system. Usually caused by non-cancerous tumors, this condition typically responds well to treatment when recognized early, allowing your cat to return to a somewhat normal life of leisure.

Typical Hyperthyroidism Symptoms

Thyroid hormones regulate your cat's metabolic rate and activity level, and too much can have your puss bouncing off the walls from excess energy. Because his system is flooded with thyroid hormones, he burns up energy faster than normal, meaning he feels hungrier more often to replace this used energy. Hyperthyroidism usually appears as an increase in appetite, activity and restlessness as he tries to use up the excess hormone in his system. Despite this ravenous appetite, he may still lose weight, as he's burning off the calories and energy faster than he can take it in.

Apathetic Hyperthyroidism

Not all cats are created equal and your kitty may be one who likes to buck the trend. A small percentage of cats who develop hyperthyroidism go the exact opposite route with symptoms, and show a decreased appetite, lethargy and depression instead of behaving like a hyperactive hummingbird. This is called apathetic hyperthyroidism, and is no less serious than the typical version. In either case, your cat would still lose weight and suffer from various health conditions caused or aggravated by the thyroid hormone excess.

Secondary Health Issues

Too much thyroid hormone racing through your cat's body poses a bigger threat to more than his waistline. Heart disease is a common complication with hyperthyroidism, as the high levels of thyroid hormone require the heart to pump faster and harder than before. The heart can become enlarged, or fluid may collect around or in the lungs. Kidney or liver problems may occur as well, due to increased drinking and litter box visits. In some cases these secondary health issues may be the downfall of your kitty, an indirect result of the out-of-control thyroid gland.


Various illnesses and conditions can lower your cat's appetite for a while, but hyperthyroidism is not a wait-and-see type of disorder. If left untreated, your cat could essentially starve himself. Treatment involves complete removal of the thyroid glands, radioactive iodine therapy or anti-thyroid medications. The first two options are one time treatments that usually resolve the problem permanently, while anti-thyroid medication requires daily pills to counter the excess released by his malfunctioning glands. Many secondary health issues resolve naturally once the hyperthyroidism is treated, but some may require treatment of their own depending on the severity of the condition.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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