Hot flashes and fatigue relieved by metformin

To describe 3 patients with long-standing hot flashes, excessive sweating, and fatigue whose symptoms were ameliorated with metformin. In this case series, we report the findings of laboratory evaluations, including assessments for thyroid, gonadal, adrenal, and pancreatic disorders, in 3 patients referred for endocrine evaluation. A 75-g oral glucose tolerance test with measurement of fasting and postprandial glucose and insulin concentrations was conducted. A trial of metformin, 500 mg twice daily, was initiated in all patients. Evaluation of factors that are associated with hot flashes and increased sweating did not establish the cause of the patients' symptoms. The 3 patients had normal glucose tolerance test results and hyperinsulinemia. Metformin therapy markedly relieved the symptoms in all patients. Hyperinsulinemia without hypoglycemia may produce a sympathoexcitatory response that manifests as hot flashes and increased sweating. Metformin may have sympathoinhibitory actions that alleviate these symptoms.