Although the U.S. Food and Drug Administration oversees the safety and effectiveness of drugs prescribed by American doctors, it does not regulate the practice of medicine. So, many medications are used “off-label,” meaning your doctor may prescribe a drug for purposes that have not yet been approved by the FDA. About 1/5 of the prescriptions for common medications are written for an off-label use, according to a 2012 review in “Mayo Clinic Proceedings.” Metformin (Glucophage), a drug licensed to treat type 2 diabetes, has a number of off-label uses.

How Metformin Works

Metformin is unlike other medications used to treat type 2 diabetes. Although all of its actions are not completely understood, metformin’s main mode of action is to decrease glucose production in your liver. In addition, metformin increases your cells’ sensitivity to the insulin released from your pancreas, which increases your body’s ability to metabolize glucose. Together, these actions reduce your blood glucose level without driving it too low. These same properties make the drug potentially useful in a number of situations.

Drug-Induced Weight Gain

Atypical antipsychotic medications, such as olanzapine (Zyprexa), are prescribed for managing schizophrenia, bipolar disorder and other conditions. But in many people, these medications cause significant weight gain, which is believed to stem from drug-induced appetite stimulation and insulin resistance.

A March 2011 analysis in the “British Journal of Clinical Pharmacology” showed people who gain weight as a result of taking olanzapine may lose some of that weight by also taking metformin. This has important implications for people whose psychiatric conditions cannot be controlled without atypical antipsychotics. Metformin may not be appropriate for everyone who takes olanzapine or similar medications.

Obesity

Obesity is by nature an insulin-resistant state. As your body mass and body fat percentage increase, so does your resistance to insulin. According to a May 2012 review in “Aging,” metformin exerts a moderate weight-reducing effect in obese people. This effect is smaller than lifestyle changes, such as a reduced-calorie diet and exercise. Nonetheless, when prescribed by a doctor, metformin may be a useful addition to anti-obesity treatment. Similarly, metformin may help address other insulin-resistant states, such as fatty liver disease and metabolic syndrome, which is sometimes called prediabetes.

Polycystic Ovary Syndrome

Up to 15 percent of reproductive-aged women suffer from polycystic ovary syndrome, which is characterized by menstrual irregularities, low fertility, obesity and high blood levels of male hormones. Scientists have discovered that many women with PCOS are also insulin resistant, which stimulates their ovaries to produce male hormones.

By increasing insulin sensitivity and decreasing the ovarian production of male hormones, metformin stabilizes hormone levels, improves menstrual regularity and possibly improves ovulation and fertility in women with PCOS. Furthermore, when women with PCOS do conceive, metformin appears to improve their chances of carrying their pregnancy to term. While metformin is commonly prescribed for women with PCOS, its use must be determined on a case-by-case basis.

Intriguing Possibilities

Given metformin’s actions in certain medical disorders, and because of what is known about its cellular and molecular activities, some researchers believe this medication may have anti-aging and anti-cancer effects. An emerging body of evidence suggests some forms of cancer and certain chronic diseases may be driven by insulin resistance. Metformin’s usefulness in these areas remains to be proven, and the FDA has not approved the drug for preventing cancer or reversing the effects of aging.