Hypothyroidism
What is it?
Hypothyroidism means the thyroid gland makes too little hormone, slowing the body's metabolism. It is usually caused by the immune system damaging the gland. It is most common in middle-aged, medium to large breed dogs.
What signs should I watch for?
Signs to watch for include weight gain without eating more; lethargy and seeking warm places; thin, dull coat or symmetrical hair loss; recurrent skin or ear infections; and darkened or thickened skin.
How is it diagnosed and treated?
Blood tests measuring thyroid hormone levels confirm the diagnosis, sometimes with additional panels. Treatment is a daily oral thyroid hormone replacement, with periodic blood tests to fine-tune the dose.
Can it be prevented, and what's the outlook?
It can't be prevented, but with lifelong treatment most dogs feel better within weeks and live normal lives.
Reviewed by the Adler Veterinary Hospital veterinary team, October 2026.
Middle-aged, medium to large breed dogs
Who's at risk:
Weight gain, lethargy, dull coat or hair loss, skin infections
Main signs:
Ongoing management with your vet
Urgency:
When to call a vet right away
- Signs coming back after treatment had been working
- Hyperactivity, poor sleep, weight loss or extra thirst while on thyroid medicine
- A head tilt, dragging the feet or poor coordination
- Repeated skin or ear infections
Not sure whether it can wait? Call us anyway. Our team can help you decide.
Source:
Related conditions
Addison's Disease
Cushing's Disease
Diabetes