Hot flashes and fatigue relieved by metformin.

Objective: To describe 3 patients with long-standing hot flashes, excessive sweating, and fatigue whose symptoms were ameliorated with metformin.

Methods: 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.

Results: 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.

Conclusions: 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.