Clomipramine is a tricyclic antidepressant (TCA) that has been used to treat various psychiatric disorders in humans for more than 30 years and, more recently, separation anxiety in dogs. TCAs have been shown to impair thyroid hormone synthesis and thyrotropin secretion, but no studies have been done in dogs. To evaluate the effects of long-term clomipramine administration on the hypothalamic-pituitary-thyroid axis, 14 healthy dogs were enrolled in this prospective study. Clomipramine (3 mg/kg PO Q 12 H) was administered to all dogs on day 0 and continued for 112 days. No adverse effects of the medication or clinical manifestations of hypothyroidism were noted during the treatment period. However, significant decreases of 35% and 38% were noted in serum total thyroxine and free thyroxine; these effects could lead to misdiagnosis of hypothyroidism. Although no evidence of hypothyroidism was noted in this study population, subclinical hypothyroidism may have occurred. Thyroid function should be carefully evaluated in dogs receiving clomipramine.

COMMENTARY: The results of this study may explain why the results of thyroid tests in patients on clomipramine may not correlate with clinical signs.

Evaluation of the effects of clomipramine on canine thyroid function tests. Guilikers KP, Panciera DL. J Vet Intern Med 17:44-49, 2003.