Metformin is the only medication in the biguanides category of blood glucose-lowering drugs approved by the U.S. Food and Drug Administration (FDA). Metformin has been available in the United States since the mid-1990s, when it received FDA approval. You may also know it by its brand name when it was under patent, Glucophage. Metformin is now widely available as a relatively inexpensive generic medication.
Metformin’s main action is to decrease the overproduction of glucose by the liver, a common problem in prediabetes and type 2 diabetes. The action of metformin helps lower blood sugar levels particularly during the night to keep fasting glucose levels under control, but it also helps control blood glucose throughout the day. Metformin also increases the uptake of glucose by your muscles. Overall, metformin decreases insulin resistance and improves insulin sensitivity, thereby helping the insulin your body still makes work more effectively.
People with prediabetes and in the early years of type 2 diabetes often continue to make some insulin, just not enough to control blood sugar levels alone. Metformin is not formally approved for use in prediabetes, and any use to treat prediabetes is considered off-label by providers.
Since its approval, metformin has become the most commonly recommended blood glucose-lowering medication to treat type 2 diabetes. In recent years it has significantly replaced sulfonylureas, such as glipizide and glyburide. Today both the American Diabetes Association (ADA), the European Association for the Study of Diabetes (EASD), and the American Association of Clinical Endocrinologists (AACE) generally recommend that people with type 2 diabetes start taking metformin when they are diagnosed to help treat insulin resistance and maximize insulin sensitivity
There are two other side benefits of metformin over the sulfonylurea category of medications: Metformin does not seem to cause weight gain (in fact, you may even lose a few pounds), and it does not cause low blood sugar (hypoglycemia) when it’s used without other blood glucose-lowering medications that can cause low blood sugar.
Metformin has also been associated in research studies with lowering risks for heart disease and some cancers in people with diabetes due to its insulin-sensitizing effects.
Metformin is approved by the FDA for use with a number of other blood glucose-lowering medications, such as insulin, glitazones (Actos, Avandia), sulfonylureas, DPP-4 inhibitors (Januvia, Onglyza, Linagliptin, and others), and GLP-1 analogs (Byetta, Victoza, Bydureon).
It’s becoming more common to put two blood glucose-lowering drugs together in a combination pill. It makes medication adherence easier, and paying for one combination medication might be less expensive than two individual ones. Metformin is often one of the medications in these combination pills along with one of the other oral medications mentioned above.