Learn about the side effects of metformin, from common to rare, for consumers and healthcare professionals. 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. 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. 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 helps manage blood sugar in type 2 diabetes. WebMD reviews common side effects, extended-release benefits, vitamin B12 risks, and precautions. Metformin is a medicine that can be used to treat type 2 diabetes, gestational diabetes and the hormone condition polyendocrine metabolic ovarian syndrome (PMOS). 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 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. 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.