Is your dog gaining weight fast? A thyroid problem?

Q: My dog, Rocky, has gained a lot of weight. I’m not really feeding him any differently. My sister said that happened to her dog, and she ended up having a thyroid problem. Should I have Rocky’s thyroid tested? R.B., Farragut

A: Yes, hypothyroidism, or low thyroid, is a possibility. The disease is more common in middle-aged or older dogs; if Rocky is 7 years old or older, your veterinarian might discuss that with you.

Significant weight gain or weight loss is certainly an indication to see your vet. Your veterinarian will do a full physical exam, including discussions regarding Rocky’s diet and exercise history. If he/she feels that thyroid testing is warranted, the recommendation for blood tests will be made.

Hypothyroidism is most commonly caused by the immune system directing the glands to function less, leading to decreased production of thyroid hormones. Thyroid cancer is rare in dogs. Dogs with hypothyroidism typically have a slowdown with their metabolism causing the weight gain.

Affected dogs may also have a dull hair coat, hair loss, lethargy and/or frequent infections.

Treatment is oral thyroid replacement therapy. Dogs typically feel better within a few weeks, although pets with weight gain and/or coat abnormalities can take a few months to return to normal. Your veterinarian will monitor the progression with blood tests until levels are stabilized. Treatment is often for life. Best of luck to you and Rocky.

If you have questions about your pet, e-mail Dr. Myers at