Metformin helps manage blood sugar in type 2 diabetes. WebMD reviews common side effects, extended-release benefits, vitamin B12 risks, and precautions. Metformin is used to treat type 2 diabetes (condition in which the body does not use insulin normally and, therefore, cannot control the amount of sugar in the blood). Metformin is in a class of drugs called biguanides. Metformin helps to control the amount of glucose (sugar) in your blood. Sign up today to receive the latest news and updates from UpToDate. © 2026 UpToDate, Inc. and/or its affiliates. All Rights Reserved. Metformin is a generic prescription medication used to help manage blood sugar levels in adults and some children with type 2 diabetes. It works by decreasing sugar production in the liver. Learn about the side effects of metformin, from common to rare, for consumers and healthcare professionals. Metformin is used together with proper diet and exercise to treat high blood sugar levels caused by type 2 diabetes. This medicine reduces the absorption of sugar from the intestines, reduces the release of stored sugar from the liver, and helps your body use sugar better. Metformin is a medicine that can be used to treat type 2 diabetes, gestational diabetes and the hormone condition polyendocrine metabolic ovarian syndrome (PMOS). Medical uses Metformin is used to lower blood glucose in those with type 2 diabetes. [15] It has also been used to help with metabolic abnormalities in polyendocrine metabolic ovarian syndrome (PMOS), and as a second-line agent for infertility in those with PMOS. [15][34] Metformin is a first-line treatment used for type 2 diabetes in adults and children 10 years and older to help improve blood sugar levels. It is also used off-label to improve symptoms of polycystic ovarian syndrome (PCOS) and other conditions. Overview: Metformin is medicine you take to help keep your blood sugar from getting too high. Common side effects may include stomach problems, such as diarrhea, nausea, vomiting, stomach pain.