Overview
Hyperthyroidism occurs when the thyroid gland overproduces hormones, supercharging the metabolism. Cats eat ravenously but lose weight, become hyperactive, and develop heart problems from the sustained metabolic overdrive. It almost exclusively affects middle-aged and older cats (typically 10+). Treatment options include medication, radioactive iodine therapy, surgery, or a prescription iodine-restricted diet.
Symptoms to Watch For
- Weight loss despite increased appetite
- Hyperactivity, restlessness, and irritability
- Increased thirst and urination
- Vomiting and diarrhea
- Unkempt, greasy coat
How Nutrition Helps
Prescription iodine-restricted diets (like Hill’s y/d) can be the sole treatment for some cats — they work by limiting the raw material the thyroid needs to produce hormones. These diets must be fed exclusively with no treats, supplements, or other foods. For cats on medication or post-treatment, balanced senior nutrition with adequate protein prevents muscle wasting.
How Activity Helps
Hyperthyroid cats are often excessively active. As treatment normalizes thyroid levels, activity returns to normal. Don’t restrict movement — the hyperactivity resolves with treatment.
Prevention Tips
- Annual blood work including thyroid panel for cats over 7
- Monitor weight — unexplained weight loss needs investigation
- Watch for behavior changes: hyperactivity, increased appetite
- Regular vet visits for senior cats
- Early treatment prevents heart damage
Breeds at Higher Risk
No strong breed predisposition, but Siamese and Himalayan cats may have slightly lower risk. Affects domestic shorthairs and longhairs equally.