Thyroid Disorders
Hypothyroidism is common in middle-aged dogs; hyperthyroidism is rare and usually cancer-related.
What is Thyroid Disorders?
The thyroid gland regulates metabolism. Hypothyroidism (underactive thyroid) is common in dogs and slows everything down. Hyperthyroidism (overactive) is rare in dogs — unlike in cats — and is almost always due to a thyroid tumour producing excess hormone.
Common signs and symptoms
Signs vary between dogs and can be subtle at first. Watch for the following, especially if several appear together or persist for more than a few days:
- Hypothyroidism: weight gain without eating more, lethargy, cold intolerance, thinning coat with symmetric hair loss, recurrent skin/ear infections, 'tragic' facial expression
- Hyperthyroidism: weight loss despite good appetite, increased thirst, restlessness, palpable neck mass
Risk factors
Certain dogs are more predisposed. Understanding risk helps you screen earlier and act sooner.
- Hypothyroidism: middle-aged medium-to-large breeds (Golden Retriever, Dobermann, Irish Setter, Boxer)
- Hyperthyroidism: senior dogs with thyroid carcinoma
When to see a vet
Use this as general triage guidance, not a substitute for veterinary advice.
- Book a routine appointment if: your dog is gaining weight without dietary changes, has a dulling coat, or seems 'slower' with age.
- Seek urgent care if: a rapidly growing lump on the neck, breathing changes, or sudden severe weight loss.
Diagnosis and management
Diagnosis is via a thyroid panel (Total T4, free T4, TSH). Hypothyroidism is treated with lifelong daily levothyroxine and regular level checks — most dogs respond within a few weeks. Hyperthyroidism management depends on the tumour type and stage.