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Wendy Brooks, DVM, DABVP
Published: August 12, 2023

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand name: Thyro-tabs 

Available in 0.1mg, 0.2mg, 0.3mg, 0.4mg, 0.5mg, 0.6mg, 0.7mg, 0.8mg, 1.0mg


The thyroid hormone represents the volume dial on one's metabolism. Too many calories are burned too fast, with subsequent heart disease not far away. Too little and the body loses energy, cannot function properly, and symptoms arise in multiple organ systems. Hypothyroidism is a classically described hormone imbalance, both in people and in dogs. 

Fortunately, hypothyroidism can be easily treated by orally providing the hormone that one's diseased thyroid gland is not adequately producing. Symptoms may take several months to resolve, depending on the organ systems affected, but generally, there is an improvement in energy and attitude after just a few weeks of treatment. The thyroid gland produces thyroxine, which is an inactive form of thyroid hormone. The body's tissues must activate thyroxine. Levothyroxine is an oral version of the hormone that the thyroid gland produces naturally.

There is a syndrome called "Euthyroid sick syndrome," whereby thyroid levels drop during times of illness as part of the body's reaction to illness. Metabolic processes slow down so the body can concentrate on healing. This is not hypothyroidism and requires no treatment.

Cats rarely become hypothyroid after treatment for hyperthyroidism. Should this occur, treatment with levothyroxine is needed to replace the hormone that is no longer being produced in adequate amounts.

How This Medication is Used 

Medication is typically given orally once or twice daily. The medication absorbs into the body best on an empty stomach. Because food alters the absorption of levothyroxine, it is best to give the medication at a similar time or times daily and on the same schedule with regard to food. Treatment is lifelong.

If a dose is accidentally skipped, do not double up on the next dose. Simply give the medication when it is next scheduled.

Levothyroxine has one use, and that is the treatment of hypothyroidism.

Side Effects 

This medication is associated with very few side effects. Most issues come from giving too high a dose and creating symptoms of hyperthyroidism: excessive thirst, appetite, and restless behavior.

Occasionally, patients on levothyroxine will experience scaly skin, ear inflammation, lethargy, or appetite loss. Any symptoms such as these should be reported to the veterinarian, but they are very uncommon and may well have another cause when seen.

Interactions With Other Drugs 

There are many medications that will interfere with thyroid tests.

Antacids may interfere with the absorption of levothyroxine. A four-hour separation between these medications is recommended. A similar situation exists with sucralfate.

Corticosteroid hormones (such as prednisolone) interfere with the activation of thyroxine into active thyroid hormone.

Concerns and Cautions

Patients with concurrent heart disease may need a dose reduction.

Expect monitoring tests to be needed when hypothyroidism is treated. 

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