Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Hypothyroid dogs are treated with levothyroxine, a thyroid hormone replacement, usually given once or twice daily for life. Your vet sets the dose based on weight and adjusts it using blood tests taken several hours after a dose. Energy often improves within a few weeks, while coat and skin improve over a few months. Signs of too much medication include panting, restlessness, increased thirst, and weight loss.
This guide doesn’t give doses.
Giving levothyroxine
- Give at the same times each day
- Be consistent about giving it with or without food, as your vet advises
- Use veterinary products or those your vet prescribes. Switching brands may change blood levels
Monitoring
- A blood test several weeks after starting or changing the dose
- Usually timed about 4–6 hours after a dose
- Periodic rechecks once stable
What to expect
- Energy and mental alertness: often within 1–2 weeks
- Weight loss: over weeks to months
- Coat and skin: over 1–3 months or more
Signs of too much medication
- Panting, restlessness, or hyperactivity
- Increased thirst and urination
- Weight loss or increased appetite
- Fast heart rate
Call your vet if these appear. If your dog chewed into a bottle, call your vet or a pet poison hotline.
What to avoid
- Stopping medication without your vet
- Using human thyroid medication without veterinary direction
Sources
- Merck Veterinary Manual: Hypothyroidism in dogs
- Scott-Moncrieff JC. Clinical signs and concurrent diseases of hypothyroidism in dogs and cats. Vet Clin North Am Small Anim Pract. 2007
- Merck Veterinary Manual: Thyroid hormones (pharmacology)
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.