Health
Sleeping more, gaining weight without eating more, glued to the radiator, thinning flanks. It may be the thyroid, or something else that looks very like it.
Caution. A very weak, cold dog with a vacant stare, a slow heartbeat or fainting, or a dog already on treatment who pants, is restless and suddenly loses weight: ring your own vet today. Do not give human thyroid tablets or supplements.
Do not look for the answer in a Facebook group, on TikTok or on a forum. Look for someone trained for this: your dog's own veterinarian, the only person who can examine, investigate and treat them.
Use this page to know what to observe, what to note and what to ask at the appointment, not to treat at home. If you still have doubts after a consultation, ask another vet or a specialist (dermatologist, internist) for a second opinion, not a group. And if you do not have a regular vet yet, find one now, while your dog is healthy: how to choose a veterinary clinic.
Your labrador is seven. He sleeps more than ever, has given up on the long Sunday walk and is putting on weight even though he eats the same as last year, maybe less. In winter he lives against the radiator. The hair on his flanks has thinned evenly on both sides, and his tail is starting to look like a rat's. Someone at the park told you, "it's his thyroid, mine had the same". It might be. Hypothyroidism is one of the most common hormone diseases in dogs and also one of the most often misdiagnosed, because it looks like ageing, like a few extra kilos and like several other illnesses. What you can do is gather the observations your own vet needs, and understand why a single blood test does not always settle the question.
Hypothyroidism develops slowly, over months, and is usually not an emergency. It calls for an appointment in the next few days, not a dash to the clinic at midnight. A few situations are the exception and need a phone call today:
Everything else (the weight, the tiredness, the coat) can wait for a normal appointment, with the notes below in hand.
The signs creep in so slowly that you get used to them. That is why the most useful thing you can do is write them down and compare with a year ago.
Weight. Weigh him now and then once a month. Write down exactly what and how much he eats, including training treats and anything from the table. A dog who gains weight on the same rations convinces a vet far faster than one who "doesn't seem to eat much".
Energy. How far he walks before he tires, how much he sleeps in a day, whether he still chases the ball, whether he is slow to get up in the morning. Look back at last year's photos and videos too; your phone remembers better than you do.
The cold. He seeks out warm spots, shivers when other dogs are fine, does not want to go out in winter.
Skin and coat. Take photos of his flanks, tail, neck and belly. Note whether the hair is falling out evenly on both sides, whether it fails to grow back where it was clipped, whether the skin has darkened or thickened or keeps getting infections. Some dogs develop a "sad" face, with thickened eyelids and forehead skin.
Ears and gait. List the ear infections from the past year: how many, how long each lasted, whether they came back soon after treatment. Some dogs with a sluggish thyroid also have weak back legs or a shuffling walk, which shows most on stairs and getting into the car. Film him from the side with your phone held low, at his height.
And the rest. Is he drinking a lot? Weeing a lot? That points more towards other hormone diseases, but tell your vet. Is he on any medication, does he have other illnesses, is he neutered?
| What you see | Hypothyroidism | Other common causes |
|---|---|---|
| Weight gain | On the same food, slowly | Eating more than you think, moving less, neutering |
| Tired, sleeps a lot | Constant, for months | Age, joint pain, heart, anaemia |
| Symmetrical hair loss on the flanks | Yes, not itchy at first | Cushing's disease, other hormone diseases, breed-related hair loss |
| Recurring skin and ear infections | Yes | Allergies, more often |
| Drinks and wees a lot | Usually not | Cushing's, diabetes, kidneys |
| Seeks warmth | Yes | Thin, old or short-coated dog |
The disease mostly turns up in dogs over four or five, of medium or large size. It is described more often in golden retrievers, Dobermanns, cocker spaniels, boxers and Irish setters, but it can affect any dog, and crossbreeds are no exception.
Ask at the practice what time, relative to the tablet, the check-up test should be taken. It varies from product to product, and a test taken at the wrong time gives a result that is hard to read.
A dog with hypothyroidism that is properly treated lives a normal life. Long walks, sport, trail work, all of it. Many owners only realise after a few weeks of treatment how much their dog had changed, because it happened so gradually they had stopped seeing it. From then on, your job is not to miss a tablet and to remember the date of the next check-up.
What dog owners search for most often on the internet about this problem, with the short answer. The answers are a guide only: the decision belongs to your dog's own vet, after an examination.
Weight gain on the same food, tiring quickly, sleeping a lot and seeking warm spots. Hair loss evenly on both flanks and on the tail, thickened or darker skin, and skin or ear infections that keep coming back. The signs come on slowly, over months, and look like ageing, so comparing with last year's photos and weights helps.
With blood tests. Usually total T4 first, then free T4 and TSH if that comes back low or borderline, plus general blood work, where cholesterol is often raised. Your vet diagnoses from all the results together and the signs. One low value is not enough, because T4 also drops in dogs ill with something else, with some medicines and in sighthounds.
It cannot be cured, but it responds very well to treatment. The missing hormone is replaced with a daily tablet for life, at a dose your vet sets and adjusts after check-up tests. Energy usually returns within a few weeks, the weight comes off over a few months, and the coat takes longest.
It is described more often in golden retrievers, Dobermanns, cocker spaniels, boxers and Irish setters, in dogs aged 4 to 10, of medium and large size. Small breeds and crossbreeds are not exempt, though. If the signs fit, any dog can be tested.
The information on this page is educational and does not replace an examination. For full details and a diagnosis, consult your dog's own veterinarian.
They often come together: the same causes, plans that complement each other.
You can no longer feel his ribs, the waist has gone, he pants after three flights of stairs. Fat creeps on and hides up close, but your hands find it in two minutes.
Tufts on the sofa are one thing. Round patches, bald flanks or a dog scratching himself raw are something else. Here is how to tell them apart.
You pick up the lead and nobody comes. He sleeps, leaves food in the bowl, ignores the ball. An off day or the first sign of illness; what comes with it decides.
Drinking like he has run a marathon, accidents indoors, panting at rest, a dropped belly. It may be more than old age: that combination has a name and can be treated.
We work with your dog's behaviour, not its health. For any sign described here, book an appointment with your own vet; the related services page explains how to choose a clinic.