Past, Present, and Future Research Avenues for Metformin: A Literature Review

Objective: To review why metformin is considered first-line therapy for type 2 diabetes mellitus (T2DM) and review newer avenues of research currently being evaluated. Data Sources: The Cochrane Library and Medline (to January 2014) were searched for case-control and cohort studies, clinical trials, and systematic reviews and meta-analyses involving metformin for any indication. Study Selection and Data Extraction: The literature search found 5 major avenues of research for metformin: reduction in mortality, delayed-onset or prevention of T2DM in the presence of prediabetes, nonalcoholic fatty liver disease (NAFLD), polycystic ovarian syndrome (PCOS), and decreased cancer risk. When available, multi-center, double-blind, controlled clinical trials or meta-analyses thereof were selected for review. If these types of studies did not exist, other types of studies were chosen for review. Data Synthesis: Metformin significantly decreases all-cause and diabetes-related mortality in overweight and obese patients with T2DM. It may also decrease risk of progression to T2DM in patients with prediabetes. Metformin has been studied for the treatment of NAFLD though data are limited. Metformin alone or combined with clomiphene may increase pregnancy and ovulation rates but has not yet been shown to increase live-birth rates in patients with PCOS. Metformin may decrease risk of colorectal cancer but not all-cancer risk. Conclusions: Metformin's clinical role in T2DM and prediabetes is well established. Other avenues of research being evaluated at this time are NAFLD, PCOS, and reduced risk of cancer; more data are needed before it has a clinical role in these indications.