Some consider Qnexa a silver bullet in the battle of the bulge — a once-a-day pill that melts away the pounds without all that bothersome exercise and healthy eating. Others consider the investigational weight-loss therapy a hollow promise, with long-term health risks outweighing the benefits of short-term weight loss.

The federal Food and Drug Administration — which rejected the drug in 2010 — will again review Qnexa on Feb. 22, taking into account additional data compiled by drug maker Vivus (Editor's note: A panel of outside experts to the FDA voted to recommend approval of Qnexa. See update below). There is a big potential market for any new diet pill — about 68 percent of adults in the United States are obese or overweight, according to the 2007-2008 National Health and Nutrition Examination Survey. And Vivus estimates more than 500 million people worldwide are obese.

Qnexa combines low doses of two FDA-approved drugs — phentermine and topiramate — in a controlled-release formulation to reduce appetite and increase satiety, the sense of feeling full.

Phentermine hydrochloride has been used as an appetite suppressant since 1959 — typically in does of 15 milligrams to 37.5 milligrams. The Qnexa formula — which comes in three doses — contains 3.75 to 15 milligrams of phentermine.

Topiramate is approved for treatment of seizures and prevention of migraine headaches in does of 100 to 400 milligrams a day. Qnexa contains 23 to 92 milligrams of topiramate.

So what are the risks and benefits of Qnexa?


Significant weight loss:

Research shows that losing 10 percent of your body weight (dropping 30 pounds if you weigh 300 pounds, for example) is likely to produce health benefits, such as improvements in blood pressure, blood cholesterol, and blood sugars, according to the Centers for Disease Control and Prevention.

The average weight loss for Qnexa patients in one study was just over 14 percent for those taking the high-dose formulation and nearly 7 percent for those taking low dose Qnexa.

Better cholesterol readings:

Those taking high-dose Qnexa saw a decrease in low-density lipoprotein lipids — LDL, or “bad cholesterol” — of about 7 percent. They also saw an 11-14 percent increase in high-density lipoprotein lipids, HDL or “good cholesterol.”

Fewer weight-related risk factors:

Those taking the drug saw decrease in blood pressure and “a lower incidence of new onset diabetes,” according to the clinical briefing document being considered Wednesday.


Rebound pounds

The clinical briefing document being considered Wednesday notes that patients who stop taking the drug gain weight.

Increased heart rate

Patients taking Qnexa experience slightly higher heart rates. There is some question if long-term use of the drug may increase the risk of a heart attack.

Birth defects

Topiramate has been associated with increased risk of birth defects, albeit in higher doses than used in Qnexa. During the course of the diet pill studies, 19 women became pregnant and gave birth. None of the children had birth defects.

Dr. Sidney Wolfe, director of Public Citizen's Health Research Group, testified before the FDA in July 2010 saying, “a large proportion of people who will use this drug will be women of child bearing age. Therefore, we strongly agree with FDA’s conclusion that there is a high likelihood of exposed pregnancies to this drug.”

Memory loss

Topiramate side effects can include memory lapses and other cognitive deficits. In arguing against approval of the drug in 2010, Wolfe told the FDA “millions of people will be using this drug. They drive. They go to school. They work. The cognitive effects, although acceptable for people who have seizure disorders, are too powerful for mainstream use as a treatment for obesity.”

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Update: A panel of outside experts to the FDA voted 20-2 to recommend approval of Qnexa on February 22, 2012.