Some evidence suggests that metformin, in combination with lifestyle changes, affects weight loss in obese children. But the drug isn't likely to result in important reductions in weight, said lead researcher Marian McDonagh.
Childhood obesity is a significant health problem in the United States, with nearly 18 percent of kids between 6 and 19 years old classified as obese. Metformin is approved by the U.S. Food and Drug Administration to treat type 2 diabetes in adults and children over 10 years old, but doctors have used it "off-label" to treat obese kids who don't have diabetes, according to background information included in the study.
McDonagh's team analyzed 14 clinical trials that included nearly 1,000 children between 10 and 16 years old. All were overweight or obese.
Based on data in adults, weight reductions of 5 percent to 10 percent are needed to decrease the risk of serious health problems tied to obesity, the researchers said. The additional amount of weight loss among children taking metformin in the review, however, was less than 5 percent on average.
"With childhood obesity on the rise -- and [its] serious long-term implications for the child's health as an adult -- clinicians and parents are searching for interventions that will provide meaningful weight reduction," said McDonagh, an associate professor in the department of medical informatics and clinical epidemiology at the Oregon Health & Science University.
"Since metformin has been used to treat type 2 diabetes for many years -- including in older children -- and often results in weight loss, it has been used off-label to treat obesity in children," McDonagh said.
The report was published online Dec. 16 in the journal JAMA Pediatrics.
Dr. David Katz, director of the Yale University Prevention Research Center, said metformin is effective at both treating and preventing diabetes.
The drug produces weight loss as a byproduct of treating insulin resistance, said Katz, who was not involved with the new research.
Insulin resistance is a condition in which the body's cells become less responsive to the hormone insulin, which helps the body control blood sugar. Insulin resistance is a step toward type 2 diabetes.
"Obese children [in the studies] were treated without specific consideration of their insulin status, which likely explains the lackluster results," Katz said. "I suspect metformin is useful in some, but not all, varieties of obesity."
In contrast, eating well and being active are effective in almost all cases of obesity, Katz said. "It seems clear the best medicine for overweight and obese kids is better use of their feet and forks, not something from a pill bottle," he said.
Dr. William Muinos, associate director of pediatric gastroenterology at Miami Children's Hospital, said he prescribes metformin only for the most obese children who are at risk for type 2 diabetes.
"In that subset of children, metformin can be very helpful in improving insulin resistance caused by increased body fat," said Muinos, who also runs the hospital's obesity clinic.
Metformin causes modest weight loss by lowering the amount of insulin the body produces and improving insulin resistance, Muinos said.
The drug should not be used for weight reduction alone, he said. "It's an adjuvant treatment, but you must start lifestyle changes," he said. "Diet and exercise -- that's the key."
For more about obesity, visit the U.S. National Library of Medicine.