# Hyperthyroidism in Cats — Treatment & Medication Reference

> Feline hyperthyroidism is the most common endocrine disorder in cats over 10 years old, caused by benign overproduction of thyroid hormone (thyroid adenoma). Untreated, it leads to weight loss, secondary cardiomyopathy, and hypertensive end-organ damage. The 4 evidence-based treatments are methimazole (oral or transdermal), radioactive iodine (I-131), thyroidectomy, and prescription iodine-restricted diet.

**Source:** Script Unlock — verified-pharmacy prescription marketplace
**URL:** https://www.scriptunlock.com/pet-condition/cat/hyperthyroidism
**Last updated:** 2026-07-05
**Reviewed by:** ScriptUnlock Pharmacy Verification Team

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## ⚠️ CAUTION

Carbimazole and methimazole can cause facial pruritis (1-3% of cats) and hepatopathy. Baseline + 2/4/8/12-week CBC/chem/T4 monitoring is the AAFP/ISFM standard.

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## Symptoms to watch for

- Dramatic weight loss despite increased appetite
- Polydipsia and polyuria (drinking + urinating more)
- Restlessness, vocalization, especially at night
- Poor coat condition, increased shedding
- Tachycardia or new heart murmur on exam

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## Treatment options for hyperthyroidism in cats

### First-line

- **methimazole** — Standard of care for daily medical management. Compounded transdermal gel applied to inner ear pinna avoids twice-daily pilling and is preferred by ISFM for cats that refuse tablets.
- **carbimazole** — Pro-drug of methimazole; used widely outside the US.




## Why compounded medication matters

Methimazole transdermal gel (compounded) is preferred over commercial tablets for chronic feline hyperthyroidism management when oral dosing is unreliable. The pinna application bypasses pill aversion and is well-tolerated long-term per the 2016 ACVIM Consensus Statement.



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## How to get treatment cheaper

1. **Upload your vet prescription** to Script Unlock: https://www.scriptunlock.com/upload-prescription
2. Verified pharmacies (retail + 503A compounding) bid the lowest cash price
3. First bid arrives in 1-4 hours
4. Pickup at the winning pharmacy or ship-to-home

**A valid veterinary prescription is required.** Always confirm diagnosis, dosing, and treatment plan with your veterinarian.

## Sources cited

- ACVIM Consensus Statement on Hyperthyroidism (2016)
- ISFM Feline Hyperthyroidism Guidelines
- Plumb's Veterinary Drug Handbook 10th ed.

## Cite this page

> Script Unlock — verified-pharmacy prescription marketplace, ScriptUnlock Pharmacy Verification Team ([scriptunlock.com](https://www.scriptunlock.com))

Last updated: 2026-07-05