CATS · OWNER EDUCATION
Hyperthyroidism in Cats
Excess thyroid hormone in cats can cause weight loss, increased appetite, increased thirst, restlessness and secondary heart or blood-pressure concerns.
THE SHORT VERSION
Understanding supports better veterinary conversations.
Feline hyperthyroidism usually develops in middle-aged or older cats and commonly involves overactive thyroid tissue. It can influence the heart, kidneys, blood pressure and metabolism.
What is this condition?
Feline hyperthyroidism usually develops in middle-aged or older cats and commonly involves overactive thyroid tissue. It can influence the heart, kidneys, blood pressure and metabolism.
Which animals can be affected?
Risk factors, examination findings and management can differ between species and individual patients.
Why can it happen?
- Overproduction of thyroid hormones by abnormal thyroid tissue.
- Most cases involve noncancerous thyroid enlargement; rare cases have other causes.
- Age and individual factors influence the likelihood of disease.
What might an owner notice?
- Weight loss despite a normal or increased appetite.
- Increased thirst, urination, restlessness or vocalization.
- Vomiting, diarrhea, an unkempt coat or a fast heart rate.
How is the problem investigated?
- Physical examination and thyroid hormone testing.
- Complete blood count, chemistry panel, urinalysis and blood pressure when appropriate.
- Additional heart or kidney evaluation based on clinical findings.
What might treatment involve?
- Veterinarian-directed medical management, therapeutic diet, surgery or radioactive iodine depending on the patient and available care.
- Monitoring of thyroid levels, kidney values, blood pressure and response to treatment.
- Selection of a treatment plan based on individual risks and household circumstances.
This is an overview, not a prescription or a recommendation for a specific individual animal.
What can owners do at home?
- Track weight, appetite, thirst, medication use and behavior.
- Follow laboratory recheck timing and handling instructions.
- Notify the veterinary team if the cat stops eating or becomes weak.
Avoid actions that could make care less safe.
- Do not give human medications, leftover prescriptions or supplements without veterinary approval.
- Do not stop, increase, decrease or double prescribed medication without contacting your veterinary team.
- Do not delay assessment if symptoms are worsening, the animal stops eating or an emergency sign appears.
What can the longer-term outlook involve?
Many cats can be managed effectively or treated definitively, but the best option depends on kidney status, heart findings, available treatment and the individual patient.
Can risk be reduced?
- There is no established universal prevention plan; regular senior-cat evaluation and early recognition improve detection.
When should you arrange care?
- Call for unexplained weight loss, increased appetite, thirst or restlessness.
Seek emergency veterinary care if you notice:
SEEK EMERGENCY VETERINARY CARE- Difficulty breathing, collapse, sudden blindness, severe weakness or rapidly worsening illness.
Sources behind this guide
Cornell University: hyperthyroidism in catsPrimary veterinary or veterinary-university guidance ↗American Animal Hospital Association veterinary guidelinesPrimary veterinary or veterinary-university guidance ↗Content last reviewed: August 23, 2026. Review status: veterinary-informed; independent veterinarian review not yet completed.