Metformin's blood glucose-lowering effects and relatively low cost make it the first drug that most providers choose and one of the most prescribed to treat type 2 diabetes. Find out if you should be taking it.

Susan Sloane, R.Ph., CDE

Metformin Facts

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.

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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.

What You Should Know About Metformin

Side Effects: You might experience abdominal bloating, nausea, or diarrhea when you begin taking metformin. For most people these symptoms go away quickly, but some people are unable to tolerate metformin.

The recommendation is for your health care provider to start off with a low dose (500 mg).This can help you minimize or avoid symptoms and determine any side effects you might have. It also helps you and your provider to track the impact on your blood sugar levels. If you need a larger dose to further lower your blood sugar, your health care provider can slowly increase the dosage. About 2,000 mg/day is the largest effective dose.

An extremely rare but potentially serious complication of using metformin is lactic acidosis. When you metabolize metformin, lactic acid is produced and can build up to toxic levels. This happens only in people with kidney disease, which is why people with significant kidney problems (increased serum creatinine level) are not good candidates for metformin.

Another reason for lactic acidosis is excessive alcohol intake or binge drinking. If you take metformin, avoid drinking more than a moderate amount of alcohol. Talk to your provider if you have concerns about the use of metformin and your alcohol intake.

Another potential risk of taking metformin is that it can cause vitamin B12 deficiency. The risk of this deficiency increases with your age, the dose of metformin you take, how long you've taken it, other medications you take, and how much vitamin B12 you eat. Vegetarians can be at a higher risk of this deficiency. Ask your health care provider about your vitamin B12 level and if you need a vitamin B12 supplement.

Taking Metformin

How to Use It: Primarily prescribed for people with type 2 diabetes, metformin may help in treating prediabetes, a health condition that can lead to type 2 diabetes. If you have prediabetes, insulin resistance, or glucose intolerance that may be related to the metabolic syndrome, your health care provider may prescribe metformin along with a lifestyle program of healthful eating and increased physical activity to slow the progression to diabetes.

Today metformin is also being used in the treatment of polycystic ovary syndrome (PCOS). PCOS is one of the most common causes of infertility in women due to a lack of ovulation. Metformin and other blood glucose-lowering medications allow many women with PCOS to resume ovulation and regain fertility in a matter of months.

Metformin is available in several forms: regularly acting tablets, extended-release tablets that allow less frequent dosing, and in a liquid form called Riomet available for people who have trouble swallowing pills.

Dosage: The tablets are usually prescribed at two daily doses of up to 2,000 mg total, typically starting with a lower dose of 500 mg. Extended-release forms are typically given once daily, but higher doses may be given twice daily for greater effectiveness at lowering blood sugar levels.

Should You Take Metformin?

These questions will help you decide if metformin can help you:

Do you have prediabetes or type 2 diabetes?

Are you having trouble controlling your blood sugar?

Are you free of liver or kidney disease?

Do you have polycystic ovary syndrome?

If you answered yes to all or most of these questions, you might want to talk to your health care provider about taking metformin.

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