Clinical Thyrotoxicosis Resulting from Liothyronine Augmentation of Antidepressant Therapy in an Adolescent.

. Thyrotoxicosis, a condition resulting from excessive peripheral thyroid hormone, is typically accompanied by thyroid function tests demonstrating a high free thyroxine (free T4) with appropriate suppression of thyroid-stimulating hormone (TSH). . We describe a 17-year-old female presenting with symptoms of thyrotoxicosis along with suppressed TSH and low free T4, a laboratory pattern concerning for central hypothyroidism. Further history revealed that she was prescribed liothyronine as an adjunct therapy for depression. . Due to the short half-life of liothyronine, clinical signs and symptoms of thyrotoxicosis may develop before detection by interval lab monitoring. . This case highlights the need for close monitoring and caution when treating adolescents with liothyronine and the importance of interpreting atypical laboratory findings within clinical context.