Prandimet (metformin/repaglinide) and metformin (Glucophage, Glumetza, Riomet) are both used to control blood sugar in people with type 2 diabetes, but they have some key differences. Prandimet is a combination of two medications, metformin and repaglinide, while metformin contains only metformin. Prandimet has been discontinued and is no longer available in the United States, whereas metformin is still widely available. Metformin works by lowering the amount of sugar your body makes and absorbs, and helps your body use its natural insulin better. It is usually taken once or twice daily and can cause stomach side effects like diarrhea and nausea, which can be lessened by taking it with food or slowly increasing your dose. Prandimet, on the other hand, combined the effects of both metformin and repaglinide to control blood sugar in two ways but is no longer an option for treatment.