Hypothyroidism: Why So Many Dogs May Be on Pills They Don't Need
In a 2024 study, specialists judged thyroid pills unnecessary for about half of 102 treated dogs. Why the diagnosis is hard, and what to ask your vet.
Written by thecanineledger
Three specialists reviewed the records of 102 dogs on thyroid medicine. They judged it “not indicated” in 58.8%, 52.9% and 45.1% of cases (Travail et al., J Vet Intern Med 2024).
The authors concluded that “hypothyroidism might be overly and incorrectly diagnosed in first opinion practice”.
While hypothyroidism is a real disease that thyroid hormone treats well, the study suggests many dogs are diagnosed on weak grounds. This page explains why the diagnosis is hard, what the study found, and what to ask your vet. If your dog is on thyroid medicine, don’t stop or change it without talking to your vet.
1. What hypothyroidism is
Hypothyroidism means the thyroid gland makes too little hormone. The study notes that dogs with the condition most often show “signs of dermatologic and metabolic diseases”: skin and coat problems, or changes such as weight gain and tiredness.
The trouble is that those signs are common for other reasons. The authors write that the signs “are often vague and nonspecific”. Because there are “no highly specific or pathognomonic clinical signs”, other illnesses “must always be considered.”
2. Why the tests mislead
No single blood test settles it. The authors write that there is no “readily‐available gold standard test” for the condition. The usual tests can be wrong both ways. Other illnesses and some medicines can lower thyroid results in a dog whose thyroid is healthy.
So the authors recommend testing “only in those dogs with a high pretest probability of the disease.” In plain terms: test a dog that looks like it has the disease, not one with a vague problem, because a low result in a dog with few signs is more likely to be wrong.
3. What the study found
The researchers searched the records of seven UK first-opinion practices for dogs on thyroid medicine, and found 102. Three specialists in internal medicine each reviewed every case.
| Specialist | “Confirmed or likely” hypothyroid | Medicine judged not indicated |
|---|---|---|
| 1 | 38.2% | 58.8% |
| 2 | 48% | 52.9% |
| 3 | 55.9% | 45.1% |
Two points stand out. Even the specialists disagreed with each other, which shows how hard the diagnosis is. And all three thought around half the dogs probably didn’t need treatment.
The study has limits. It looked back at records, at seven practices, in one country. The authors declare no conflicts of interest, and the study received no funding.
Our note: This is one study of 102 dogs in UK practices. We didn’t look for studies from other countries.
4. Why it matters
Treatment isn’t harmless. The authors write that “there seems to be a perception that levothyroxine supplementation is “safe,"" but that “this is not necessarily the case”. Too much can cause side effects, or shrink the thyroid in a dog that never needed treatment.
There may be a second cost, though the study didn’t measure it. If the real cause of a dog’s signs is something else, such as allergies or another illness, it may go untreated while the dog takes thyroid pills.
Our note: We haven’t read a source on how a vet checks whether a dog already on treatment still needs it. Ask your vet before changing anything.
5. What to ask your vet
- What signs made you suspect hypothyroidism?
- Which tests were done, and could another illness or medicine have affected them?
- Did my dog’s signs improve on treatment, and how did we measure that?
- If we’re unsure, how could we find out whether my dog still needs it?
6. What we could not verify
| Commonly said | What we found |
|---|---|
| “A low thyroid result means hypothyroidism” | Not on its own. Other illnesses and medicines can lower results. |
| “Thyroid pills are harmless, so worth a try” | Not necessarily, the study’s authors say. |
| “Hypothyroidism is very common in dogs” | Unknown. The study notes that its prevalence “remains unknown.” |
Sources
- Travail V, Fernandez Sanchez C, Costo JM, et al. Assessment of the likelihood of hypothyroidism in dogs diagnosed with and treated for hypothyroidism at primary care practices: 102 cases (2016–2021) (J Vet Intern Med 2024; retrospective study; full text read)
Always confirm with your vet before acting on anything on this page.