Hypothyroidism in Labrador Retrievers, Explained

A Lab who’s gaining weight on the same food, sleeping more than usual and losing hair on the tail is easy to write off as “getting older.” Sometimes that’s true. Sometimes it’s the thyroid. Hypothyroidism in Labrador Retrievers means the thyroid gland isn’t making enough hormone, so the whole body runs slower than it should.

The good news first. It’s one of the most treatable hormone problems in dogs, usually with a daily pill and a few blood tests a year. I’m not a vet, so treat this as a guide to what to look for and what to ask, and let your vet handle the diagnosis.

What the thyroid does

The thyroid is a small gland in the neck. Its hormones set the pace of the body’s metabolism, which affects energy, weight, body temperature, skin, coat and even heart rate. When hormone levels drop, almost every system slows down a little. That’s why the signs are so varied, and why they creep in gradually rather than appearing overnight.

Hypothyroidism is a lack of thyroid hormone. The opposite problem, an overactive thyroid, is rare in dogs, though it’s common in cats. I’ll come back to one surprising cause of it later.

Why Labs get hypothyroidism

According to VCA Animal Hospitals, two diseases cause more than 90% of hypothyroidism in dogs. Both slowly destroy the gland’s ability to make hormone.

I’d sum up the two main causes like this:

• Lymphocytic thyroiditis. The immune system attacks the thyroid by mistake. This is the most common cause, and it’s believed to be inherited.
• Idiopathic thyroid atrophy. The gland’s normal tissue is gradually replaced by fat, for reasons nobody fully understands.

The autoimmune form often starts years before any signs show. The Orthopedic Foundation for Animals (OFA) notes that autoimmune thyroiditis usually appears at 2 to 5 years of age, and that dogs can seem normal for years while the gland is being damaged. By the time a Lab looks unwell, most of the thyroid is often already gone.

How common it is in Labradors

Hypothyroidism is one of the more common hormone disorders in dogs, but it’s still not something most dogs get. A large 2022 VetCompass study of 905,553 dogs under UK veterinary care found about 0.23% of dogs had a hypothyroidism diagnosis in a year. It also found 24 breeds with higher odds than crossbred dogs, and the Labrador was one of them.

Here’s how Labs compared with some other breeds in that study:

Labs have a raised risk, but a modest one. The large number of cases mostly reflects how many Labs there are. Based on my research, that’s the pattern across most Lab health data: a common breed racks up a lot of cases even when its individual risk is only slightly raised. If you have a Golden mix, like a Goldador, I’d keep the thyroid even higher on your radar.

Which Labs are most at risk

The same study looked at more than breed. The average age at first diagnosis was about 7.65 years, and risk climbed with age. It also rose with adult body weight.

Factors that raised the odds in that study included:

• Older age (dogs 11 to 13 were about 4.5 times as likely to be diagnosed as dogs 5 to 7)
• Being neutered, for both males and females, compared with intact females
• A heavier adult body weight
• A family history, since the autoimmune form is heritable

One caution about weight. The researchers couldn’t say which came first, the weight or the thyroid. Both are plausible. It’s one more reason I’d keep a Lab lean, and one more reason not to blame every extra pound on the thyroid.

Signs of hypothyroidism in Labrador Retrievers

The signs are slow, vague and easy to mistake for aging. No single sign proves anything. What matters is a pattern, especially several of these together in a middle-aged Lab.

These are the signs VCA lists as most common, with what you might notice at home:

The cold one stands out to me. I’ve seen plenty of Labs flop down in the snow happily. A Lab who suddenly avoids cold weather is worth a closer look, because most Labs are happy in the cold. My guide on how cold Labradors can handle covers what’s normal.

Less common signs can show up too. I’d keep these on your list even though they’re rarer. VCA mentions:

1. A “sad,” puffy face.
2. Weakness, wobbliness, a head tilt or facial nerve problems.
3. Reduced fertility, or changes in a female’s heat cycles.
4. Dry eye or fatty deposits on the cornea.
5. A slow heart rate and high cholesterol on bloodwork.

Book a vet visit if you notice several of these together, or if any single sign is getting steadily worse. Thinning hair can also come from normal seasonal shedding, which my post on whether Labs shed explains, so a pattern matters more than one bald patch.

When it’s probably not the thyroid

Here’s where I’d be careful. Most overweight Labs don’t have a thyroid problem. They’re eating more calories than they burn, often thanks to a gene variant that makes many Labs extra hungry, and generous treats.

Signs that point away from the thyroid:

• Gaining, but still bright and playful
• The coat is healthy and shiny
• Weight comes off when you cut portions and treats
• Your Lab begs constantly (hypothyroid dogs often aren’t extra hungry)

If that sounds like your dog, a measured diet is the first step. My guide to Labrador weight and growth explains how to body condition score your Lab by feel. Still ask your vet if you’re unsure, because a simple blood test settles it.

How vets diagnose hypothyroidism

Diagnosis is less straightforward than people expect. One low thyroid number doesn’t confirm the disease, because illness and some medications can lower thyroid hormone in a dog whose thyroid is perfectly healthy. Large breeds also tend to have lower normal levels than small ones.

This is the usual order of testing, based on VCA and veterinary guidelines:

1. A physical exam and routine bloodwork.
2. Total T4 (TT4). A screening test. A normal result makes hypothyroidism unlikely.
3. Free T4 by equilibrium dialysis. A more accurate test that’s less affected by other illness.
4. TSH. A high TSH alongside a low T4 strengthens the diagnosis.
5. A full thyroid panel, including thyroglobulin antibodies, if the picture is still unclear.

Tell your vet about every medication and supplement your Lab takes. Steroids and some seizure medications can lower thyroid results, and so can a recent illness, which is why some vets retest after a dog has recovered.

Treatment for a hypothyroid Lab

Treatment is a synthetic thyroid hormone called levothyroxine, given by mouth. VCA puts it plainly: hypothyroidism is treatable but not curable, so the pill continues for the rest of your dog’s life.

Your vet will pick the starting dose based on your Lab’s weight, then adjust it from blood tests. Never change the dose yourself or use human thyroid medication. VCA says levels are usually checked about a month after starting, timed around the pill, and then rechecked roughly every six months.

Too much hormone can cause problems too. Call your vet if you see these after starting treatment:

• Restlessness or hyperactivity
• Trouble sleeping
• Weight loss
• Drinking much more water than usual (I’d note how often you refill the bowl)

The dose is usually easy to fine-tune. Most dogs settle on a stable dose within a few rechecks.

What improvement looks like

Patience helps here. Energy usually comes back first, and the coat comes back last. Veterinary sources describe most signs improving within about 4 to 6 weeks, with skin and coat changes taking months.

Here’s a rough timeline of what owners can expect:

If things aren’t improving on that sort of timeline, go back to your vet. The dose may need adjusting, or something else may be going on. Recurring ear and skin infections sometimes need their own treatment even once the thyroid is under control, and my post on Labrador ears covers routine ear care.

Living with a hypothyroid Lab

Once the dose is right, most hypothyroid Labs live a normal, active life. I find that the most reassuring part of the whole diagnosis. The daily routine changes very little. The main jobs are the pill, the blood tests and keeping weight in check.

These habits make it easier:

• Give the pill at the same times each day, with or without food, but consistently
• Set a phone reminder, because a missed week shows
• Keep a simple log of weight and energy to share at rechecks
• Weigh food portions, and adjust them as the metabolism picks back up
• Build exercise back up gradually

Exercise matters, but ease into it. A Lab who’s been sluggish for months won’t have the fitness for long hikes right away. My guide on how much exercise a Labrador needs has a sensible target to work up to.

Tell any new vet, groomer or boarding kennel about the diagnosis. If your Lab ever needs surgery, the medication and recent results belong in the plan.

Thyroid screening for breeding Labs

Because the autoimmune form is inherited, screening matters for anyone breeding Labs. The OFA thyroid database tests for thyroglobulin autoantibodies, which usually appear before any clinical signs. A dog can get an OFA thyroid number if normal at 12 months, and OFA recommends retesting at ages 2, 3, 4, 6 and 8.

If you’re buying a puppy, it’s fair to ask whether the parents have been thyroid tested. It isn’t always part of the core Lab health tests, so I wouldn’t rule out a breeder just because they haven’t done it. A breeder who knows the family’s thyroid history is a good sign, though. My post on Labrador health issues covers the main tests to ask about.

Questions I’d ask at the vet visit

When I go into a vet visit with a worry like this, I write my questions down first, because it’s easy to forget them in the exam room. A short list makes the appointment far more useful. These are the ones I’d bring:

• Which thyroid tests are you running, and is total T4 enough on its own?
• Could another illness, or any of my dog’s medications, be lowering the result?
• If the result is borderline, should we retest later instead of starting treatment?
• When will we recheck levels, and how should I time the pill before that blood draw?
• Which signs should improve first, and by when?

I’d also bring my log of weight and energy, plus photos of any coat changes. Photos help a vet see a slow change that’s hard to describe from memory.

A thyroid problem you can cause with food

Here’s a twist I didn’t expect when I started reading about thyroid disease. Some dogs get an overactive thyroid from what’s in the bowl. In 2017 the FDA warned about certain beef-based dog foods and treats that contained thyroid tissue from the gullet, which caused hyperthyroidism in dogs who ate them. The dogs recovered once the food was stopped.

It’s rare, but it matters for two groups of Labs. Raw-fed dogs eating “gullet” or “weasand” chews, and dogs on homemade diets with organ meat, can take in thyroid hormone without anyone realizing. If your Lab is restless, losing weight and drinking more, mention the diet and chews to your vet.

Skip the over-the-counter thyroid supplements

You’ll see “thyroid support” chews and glandular supplements sold online. I’d avoid them unless your vet specifically recommends one. Some glandular products contain actual thyroid tissue, so the hormone dose is unknown and can interfere with blood tests or prescribed treatment.

A Lab with a real thyroid problem needs a diagnosis and a measured prescription. A Lab without one doesn’t need thyroid support at all.

FAQ

My last word on thyroid problems

From my experience reading up on this condition, the hardest part is noticing it at all. Trust the gut feeling that your Lab “isn’t quite himself” and ask for bloodwork. A daily pill is a small price for getting your dog back.