A 21-year-old woman was admitted to the emergency department with palpitations and chest tightness. Fifteen hours earlier, the patient had ingested 200 levothyroxine tablets (10 mg), more than 10 clonazepam tablets (20 mg), and 20 zolpidem tablets (200 mg), after mental stimulation. The patient's parents reported that she had been diagnosed with hypothyroidism due to fatigue 3 years ago and was being treated with levothyroxine (12.5-25.0 µg/d) without thyroid function monitoring. In addition, she was diagnosed with depression 2 years previously and was taking clonazepam and zolpidem for intermittent treatment. Her family history included maternal hypothyroidism. On admission, the patient was conscious, presenting with palpitations, dyspnea, dizziness, fatigue, and sweating but with no nausea, vomiting, abdominal pain, nor diarrhea. Her vital signs were a temperature of 37.3 ºC, heart rate of 103 beats/min, blood pressure of 100/73 mmHg, respiratory rate of 27 breaths/min, and oxygen saturation of 95% while breathing room air. The thyroid gland was Ⅰ degree swollen, tough, and without tenderness. The patient’s thyroxine (T4) level was > 320 nmol/L, free thyroxine (FT4) level was > 100 pmol/L, triiodothyronine (T3) level was 6.27 nmol/L, free triiodothyronine (FT3) level was 27.96 pmol/L, thyroid stimulating hormone (TSH) level was < 0.01 mIU/mL, thyroglobulin antibody (TGAb) level was 583.4 IU/mL, thyroid peroxidase antibody (TPOAb) level was 30.8 IU/mL, and thyrotropin receptor antibody (TRAb) level was < 0.3 IU/L. Chemistries were within normal limits, except for an alanine aminotransferase level of 74.3 U/L (normal range: 7-40 U/L). There was no imaging examination.