Hypothyroidism in Dogs

Many are Simple to Manage, Others are a Challenge. Nearly all do Well


My 10-year-old spayed lab cross has been hypothyroid for 2 1/2 years. Molly’s thyroid is still not stable and she’s been on different levels of levothyroxine, countless blood work and now on phenobarbital for seizures. She is healthy in every other way. I just don’t understand and would like to get Molly better and stable.

Dr. Nichol:

Hypothyroidism (low thyroid disease) is common and, in most dogs, similar to Hashimoto’s thyroiditis of humans. Fortunately, the majority of dogs respond well to treatment. The others can be complicated.


There are many possible symptoms of low thyroid hormone levels including mental dullness, obesity, thin hair coat, and heat-seeking behavior in cold weather. Dogs with skin and ear diseases, eye problems, infertility, and neurologic symptoms including seizures and aggression are also suspect.


It’s best to confirm Molly’s diagnosis with a full thyroid blood panel including a relatively new test called FT4 (ED). Follow-up tests may also be needed to determine the best medication. Unfortunately, many diseases can cause low test results in dogs whose thyroid glands are actually normal. Molly’s seizures may be the result of poorly controlled thyroid levels, epilepsy, or more serious problems. This girl needs in-depth care. If her doctor wants extra help, a referral to a specialist might be best.