Canine Thyroid Medication Side Effects

Canine thyroid medication can reduce all symptoms of hyper- or hypothyroidism in your dog, but they can also lead to several side effects. Many side effects are common and will go away once your dog has adjusted to the medication. However, address any concerns with your veterinarian.

Thyroid Treatment

The thyroid gland is responsible for producing hormones T3 and T4, which regulate and affect many bodily functions in our dogs, including growth, metabolism and fat breakdown. Hyperthyroid disease occurs when your dog's body produces too many hormones, and hypothyroid disease occurs when it doesn't produce enough. Of the two, hypothyroidism is much more common.

Both hyperthyroid and hypothyroid disease are most commonly treated with medication, administered twice daily. For hyperthyroidism, the focus is on reducing the amount of hormones produced, while in hypothyroidism, the pills prompt the body to produce additional T4. Because the body uses these hormones so quickly, a pill is usually required twice each day.

Side Effects of Hypothroid Medication

Symptoms of hypothyroidism include:

  • lethargy
  • weight gain
  • dull coat
  • skin infections
  • diarrhea or constipation
  • cold intolerance
  • various skin disorders, such as odor, greasy skin or dry skin.

Hypothyroidism can also cause behavioral changes such as increased reactivity or aggression.

Side effects of medication can often increase these problems initially, including weight gain, loss of appetite, nausea, diarrhea and drowsiness. Additional side effects include dry mouth, dizziness, difficulty sleeping, vomiting, rash or personality changes. If your dog has an allergic reaction, you may see swelling around the face or tongue, difficulty breathing or hives. If this happens, consult your veterinarian immediately.

Mild side effects will usually subside after a few weeks or months, and your dog will regain his regular energy level and appetite, just as he had before developing thyroid disease.

Side Effects of Hyperthyroid Medication

Symptoms of hyperthyroidism are basically opposite of hypothyroidism. Though you may see similar skin disorders and dull coat as with hypothyroidism, additional symptoms include dramatic weight loss paired with increased appetite and behavior changes such as anxiety and hyperactivity. Your dog may also drink a lot more and may suffer from vomiting or diarrhea.

Treatment of hyperthyroidism inhibits production of thyroid hormones rather than stimulating them, so side effects may include symptoms of hypothyroidism, such as weight gain and lethargy. Additional side effects include anorexia and vomiting.

Serious side effects include:

  • fever
  • chills
  • easily bruising or bleeding
  • weakness
  • blood in urine or stools
  • blistering
  • dark urine
  • jaundice

Consult your veterinarian if your dog experiences any serious symptoms or an allergic reaction similar to that described for hypothyroid disease medication.

Thyroid disease is the most common endocrine disease affecting dogs, so many dogs deal with some type of thyroid disease in their lifetime. Some breeds, such as Golden Retriever, Great Dane, Beagle, Cocker Spaniel, Labrador Retriever, Rottweiler, Boxer, Doberman and German Shepherd, are more susceptible. However, treatment is highly effective once your pet adjusts to the new medication.