The present invention is based on the unexpected discovery that a combination of certain known drugs exhibits synergistic effects in treating metabolic syndrome and various other diseases. In particular, the invention comprises a pharmaceutical composition comprising: (1) a therapeutically effective quantity of a first agent that is an AMPK activator； and (2) a therapeutically effective quantity of a second agent that possesses or maintains serotonin activity. A preferred composition comprises metformin hydrochloride and melatonin. The invention further comprises methods for the use of these compositions for the treatment of metabolic syndrome, hyperproliferative diseases including cancer, and other diseases and conditions.
