Brazilian researchers are presenting the results at The Endocrine Society's 93rd Annual Meeting in Boston.

Among more than 3,300 overweight or obese patients, those who took topiramate for at least four months lost 11.8 pounds more on average than individuals who took "dummy" pills, or placebo, found the meta-analysis, a systematic and quantitative review of published studies.

"Topiramate is not an approved drug for the treatment of obesity. Data from individual clinical trials might not be sufficient to support physicians' decision to prescribe it for this use, and robust evidence of its safety is lacking," said lead investigator Caroline Kramer, MD, PhD. She is an endocrinologist at Clinic Hospital of Porto Alegre in Brazil.

Currently topiramate is approved as an anti-convulsant for treatment of seizure disorders and for prevention in adults of migraine headaches.

The investigators pooled the research results of 10 randomized, controlled clinical trials (considered the gold standard in scientific research) that evaluated the benefits and adverse effects of topiramate prescribed for weight loss. They analyzed data about the effectiveness of topiramate on weight loss in 3,320 patients and data on adverse effects in 6,620 patients, she said.

According to the analysis, the duration and dosage of treatment affected the weight-loss benefits. Weight loss was higher when the drug was prescribed at doses of 96 to 200 milligrams per day for more than 28 weeks compared with less than 28 weeks, the authors reported. Compared with study subjects who took the placebo, topiramate-treated patients were seven times likelier to lose more than 10 percent of their body weight.

However, the authors found that patients were nearly two times more likely to stop topiramate treatment because of side effects than were those receiving placebo. The most common side effects, according to Kramer, included a burning sensation (paresthesia), typically around the mouth; impaired taste; and psychomotor disturbances, including slower thinking and reduced physical movements. Difficulty concentrating and memory impairment also were increased.

"Topiramate has a substantial effect on weight loss, at least comparable to the weight loss that other anti-obesity drugs induce," Kramer said. "We have so few pharmacological options for the treatment of obesity that I believe topiramate can be a useful tool together with diet and exercise."

She said it is important, however, for patients to understand the drug's known possible side effects and to be aware that it may have uncommon side effects that researchers have not yet observed.

The National Institutes of Health caution that people should use prescription weight-loss medications only if they are at increased risk of health problems because of their excess weight.

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