Thyroid hormones are sometimes used for purposes for which they are not approved. Reasons for off-label use can be overweight, prevailing depressive mood, or various somatic symptoms. Information about the intake of thyroid hormones in order to lose weight can be easily obtained from inappropriate/nonmedical websites. The objective of this case report is to describe the first case of a lethal abuse of liothyronine. The case was a 29-year-old male (BMI 32) without relevant illnesses. An autopsy was performed and followed by histological, toxicological, and clinical chemistry examinations. The autopsy revealed no relevant pathology. Histology showed multiple areas of focal cell necrosis in the myocardium and signs of acute heart failure including severe edema of the lungs; the follicles of the thyroid gland were markedly plump. Postmortem laboratory results indicated lethal liothyronine intoxication. Despite prevailing opinion, uncontrolled intake of liothyronine can cause lethal thyroid storm in a euthyroid patient without manifested cardiac illnesses.