Hypothyroidism in Cats: Expert Vet Guide 🐱❄️ 2025

By Dr Duncan Houston BVSc, veterinarian & founder of Ask A Vet.

Hypothyroidism is a rare condition in cats where the thyroid gland produces too little thyroid hormone, leading to a slowed metabolism and wide-ranging health effects. This guide explores:

• 🧬 What is feline hypothyroidism (primary, congenital, iatrogenic)?
• 🚨 Recognizing key symptoms early
• 🔍 Diagnosing through labs & imaging
• 💊 Effective treatment strategies
• 📆 Long-term care, monitoring & nutrition
• 🤝 Support via Ask A Vet, Woopf & Purrz

🔍 What Is Hypothyroidism?

Hypothyroidism occurs when the thyroid gland fails to produce enough hormone (T4/T3). In cats, it is far less common than hyperthyroidism—most cases are iatrogenic, following treatment for hyperthyroidism, such as surgery, radiation, or anti-thyroid medication :contentReference[oaicite:2]{index=2}.

Types in Cats

• Primary acquired: Destruction due to lymphocytic thyroiditis or atrophy, extremely rare :contentReference[oaicite:3]{index=3}.
• Congenital: Rare kitten disorder causing dwarfism, neurological signs, and lethargy :contentReference[oaicite:4]{index=4}.
• Iatrogenic: Most common type—resulting from treatment of hyperthyroidism (thyroidectomy, radioiodine, or methimazole) :contentReference[oaicite:5]{index=5}.

🚨 Signs & Symptoms

Common signs include:

• 🐢 Lethargy, inactivity, mental dullness :contentReference[oaicite:6]{index=6}
• 📍 Weight gain despite low appetite, mild obesity :contentReference[oaicite:7]{index=7}
• 🧣 Poor coat quality—matted, dull fur, hair loss :contentReference[oaicite:8]{index=8}
• 🌡️ Cold intolerance or low body temperature :contentReference[oaicite:9]{index=9}
• ⚠️ Bradycardia (slow heart rate), intolerance to activity :contentReference[oaicite:10]{index=10}
• 🚶‍♀️ Constipation, decreased gastrointestinal motility :contentReference[oaicite:11]{index=11}

In congenital cases, kittens show developmental delays, dwarfism, seizures, and persistent kitten coat :contentReference[oaicite:12]{index=12}.

🧪 Diagnosis

• History/exam: previous hyperthyroidism treatment or congenital signs.
• Blood tests: low total T4 with high TSH suggests primary; free T4 helps confirm :contentReference[oaicite:13]{index=13}.
• TSH assay: to detect primary disease.
• CBC/biochemistry: check for cholesterol, liver/kidney issues :contentReference[oaicite:14]{index=14}.
• Congenital work‑up: thyroid hormone panels, radiographs, neurology for kittens.

💊 Treatment

Lifelong thyroid hormone replacement is effective and typically safe:

• Levothyroxine: daily oral tablets tailored by weight; adjust based on T4 & TSH every 6–8 weeks :contentReference[oaicite:15]{index=15}.
• Congenital cases: early levothyroxine improves growth and neurological outcomes :contentReference[oaicite:16]{index=16}.
• Monitor: T4 & TSH 4–6 hours post-pill; check organs every few months.

📅 Long-Term Care & Monitoring

• Retest thyroid levels after 6–8 weeks of therapy, then every 6 months
• Regular weight checks—adjust dose for growth or weight change
• Manage comorbidities (e.g. kidney, liver disease) alongside thyroid treatment
• Support overall well-being with balanced nutrition

🏡 Nutrition & Lifestyle

• Balanced diet: moderate calories to prevent obesity
• Grooming support: keep coat brush and mat-free
• Warm environment: support cold-intolerant cats
• Activity: gentle exercise to maintain muscle mass

🤝 Role of Ask A Vet, Woopf & Purrz

Ask A Vet offers telehealth check-ins for lab review, dosing advice, and symptom tracking. Woopf & Purrz provide high-quality nutrition options to maintain ideal weight and coat health—great support for hypothyroid cats.

🔑 Key Takeaways

• Hypothyroidism is rare in cats—usually due to previous treatment of hyperthyroidism.
• Look for subtle signs: lethargy, weight gain, poor coat, cold sensitivity.
• Diagnosis through T4, TSH, and history.
• Lifelong levothyroxine therapy works well with proper monitoring.
• Support with tailored nutrition, telehealth, and regular veterinary care.

📞 Final Thoughts

Although uncommon, feline hypothyroidism is manageable with early detection and consistent care. With hormone replacement, thoughtful nutrition, and Ask A Vet’s support, your cat can enjoy a long, comfortable life 😊.

Have questions about dosing, lab results, or your cat’s energy? Visit AskAVet.com and download the Ask A Vet app now!