Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Thyroid problems in dogs are rarely emergencies, but a few situations need urgent care: myxedema coma (a rare, severe form of hypothyroidism causing extreme weakness, low body temperature, and dullness), thyroid tumors that cause a neck mass, breathing or swallowing trouble, or bleeding, and thyroid medication overdoses from a dog chewing into a bottle.
Myxedema coma
- Profound weakness or collapse
- Very low body temperature without shivering
- Dullness or unresponsiveness
- Slow heart rate
- Swelling of the face and skin
This is rare but life-threatening. Go to an emergency vet.
Thyroid tumors
- A firm lump in the neck, below the jaw or near the windpipe
- Difficulty breathing or swallowing, cough, or voice change
- Some cause signs of an overactive thyroid
See your vet promptly for any neck lump. Breathing difficulty is an emergency.
Medication overdose
A single large levothyroxine ingestion is usually less dangerous than people fear, but it can cause restlessness, panting, vomiting, and a fast heart rate. Call your vet or a pet poison hotline for advice: ASPCA Animal Poison Control Center (888) 426-4435 or Pet Poison Helpline (855) 764-7661 (fees apply).
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 tumors in dogs
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.