Cat Hyperthyroidism Treatment in San Jose — ARCH Veterinary

What is feline hyperthyroidism?

An overactive thyroid gland (almost always a benign tumor called an adenoma) produces too much thyroid hormone. The metabolism revs up, leading to weight loss despite a strong appetite, vomiting, hyperactivity, and a higher heart rate. Untreated, it damages the heart and kidneys.

Classic signs in San Jose cats we see

Weight loss with a ravenous appetite, vomiting or diarrhea, increased thirst and urination, restlessness or yowling at night, unkempt or greasy coat, fast heart rate, and a palpable thyroid nodule in the neck. Many owners notice the weight loss first.

Diagnosis at ARCH

Bloodwork including total T4, free T4 if needed, full chemistry panel, CBC, urinalysis, and blood pressure measurement. We always screen for concurrent kidney disease — treating hyperthyroidism can unmask hidden CKD, so we plan treatment accordingly.

Treatment options

Methimazole (oral or transdermal gel) is the most common first-line treatment and works well long-term with monitoring. Hill's Y/D iodine-restricted diet is an option for some single-cat households. I-131 radioactive iodine is the gold-standard cure and we coordinate referrals to specialty centers. Surgical thyroidectomy is rarely used now.

Monitoring and long-term outlook

After starting treatment, we recheck T4, kidney values, and blood pressure at 2–4 weeks, then every 3–6 months. With consistent monitoring, most hyperthyroid cats live for years with good quality of life.

Advanced veterinary care in San Jose

ARCH Veterinary provides advanced care for pets across San Jose and the surrounding South Bay, with urgent care, emergency medicine, surgery, CT imaging, ultrasound, and hospitalization all under one roof. Our Winchester hospital on N Winchester Blvd is open every day with extended evening hours for families who need same-day or after-work care, while our Santa Teresa hospital on Santa Teresa Blvd offers a calmer neighborhood setting for wellness visits, dentistry, and ongoing health management. Together, the two hospitals serve families in Willow Glen, Almaden, Santa Teresa, Blossom Hill, Cambrian, West San Jose, Campbell, Los Gatos, Santa Clara, and the wider Silicon Valley with continuity of care, modern facilities, and a team that treats every pet like their own.

Frequently asked questions

What's the first sign of hyperthyroidism in cats?

Weight loss despite a strong (often ravenous) appetite is the classic early sign. Vomiting and restlessness often follow.

Is hyperthyroidism curable?

I-131 radioactive iodine therapy cures most cases. Methimazole controls the disease but must be given for life.

What age does it start?

Almost exclusively in cats over 8, with most diagnoses between 12–15 years.

Will treatment hurt my cat's kidneys?

Treating hyperthyroidism can reveal underlying kidney disease that was masked. We always check kidney values before and during treatment.