Low energy and weight gain can suggest hypothyroidism, but they are also common with aging, pain, diet changes and other conditions. The best time to bring up thyroid concerns is when you notice a persistent pattern—not after treating your dog with a supplement based on a symptom checklist.
Book an appointment for gradual changes
Unexplained weight gain, reduced stamina, excessive shedding or thinning coat, recurring skin or ear disease, and unusual cold-seeking are worth discussing with a veterinarian. Most dogs with acquired hypothyroidism develop signs gradually, often in middle age. Bring a record of weight, eating habits and existing medications.
What happens during testing
The clinician considers the overall examination and may order blood and thyroid tests. Total T4 by itself can be misleading: medication, nonthyroidal illness and breed can lower it. Free T4 and TSH are sometimes used to clarify the diagnosis. Do not start levothyroxine from another pet’s prescription or a general online dosing chart.
Which changes need urgent care?
Collapse, seizures, severe weakness, trouble breathing or an abrupt inability to walk are not symptoms to monitor for several days while waiting for thyroid tests. Seek prompt emergency veterinary assessment. Sudden serious symptoms often have causes other than routine uncomplicated hypothyroidism.
Follow up when already on medication
If a treated dog becomes unusually restless, pants excessively, loses weight unexpectedly or has gastrointestinal signs, call the prescriber. Those signs can have several causes, including too much thyroid replacement. For context read thyroid symptoms and treatment monitoring.
Veterinary references
- AAHA: Canine hypothyroidism
- AAHA: Diagnostic testing and monitoring
- FDA: Approved treatments for hypothyroidism in dogs
For education only. Thyroid tests and treatment must be interpreted by a veterinarian.
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.