03/07/2012 04:19 pm ET

Qnexa Diet Pill: Making A Weight-Loss Drug That Doesn't Sicken You Is Apparently Difficult

Drug companies and doctors have searched more than six decades for a diet pill that really works and isn't dangerous. A new drug called Qnexa is the latest contender, but critics are raising huge red flags about health risks.

The U.S. Food and Drug Administration is set to decide within weeks whether to okay the drug, billed as the first new weapon to combat obesity in more than a dozen years.

The stakes are enormous. A diet pill that actually helps people lose weight without exposing them to harmful side effects is like the Holy Grail for drug companies hunting for the next blockbuster medication. And rising obesity rates provide a customer base hungry for a quick fix. More than 78 million Americans aged 20 and older -- or 36 percent -- were obese in 2010, according to the Centers for Disease Control and Prevention. With a market so large, Qnexa sales could rival the more than $10 billion a year generated by Pfizer's record-setting cholesterol drug Lipitor, one Wall Street analyst told Bloomberg News.

No diet pill has ever come close to these numbers. The pile-up of failed and often dangerous drugs is legion, beginning with the use of amphetamines in the 1950s. Qnexa is a descendent of an amphetamine called desoxyephedrine that was cleared by the FDA in 1947.

That drug is now more commonly known as methamphetamine.

"I don't know how many of these drugs are going to have to come off the market," said Sidney Wolfe, a physician and the director of Public Citizen's Health Research Group, "before someone wakes up." The consumer group has raised alarms over the years about diet drugs like "fen-phen," Redux, and Meridia, which were later yanked off the shelves when evidence emerged that they were dangerous, or even deadly.

Research presented to the FDA by Vivus, the company developing Qnexa, shows why the drug has a shot at approval: patients in a study lost an average of about 10 percent of their body weight in a year. Qnexa also lowered blood pressure. But the study revealed the drug, like past diet pills, can cause heart palpitations and increased heart rate, which can lead to heart attacks or strokes. Past research has also linked one of its ingredients to birth defects. A Vivus spokeswoman declined to comment.

Qnexa's critics foresee more disappointment and possibly another disaster. The cardiovascular side effects associated with the drug are too similar to those that have been banned, and the weight-loss effects too meager, to justify subjecting patients to the dangers, Wolfe said.

The weight-loss drugs currently available haven't lived up to their billing. The fat-blocking drug orlistat, sold with a prescription as Xenical and over-the-counter as Alli, is available but has side effects that include flatulence and loose, oily bowel movements, so it hasn't been a success, said Dharam Kumbhani, a cardiologist at Brigham & Women's Hospital in Boston.

Considering the risks and the spotty history of diet pills, why do drug companies, doctors and the FDA keep trying? Because obesity itself is a serious medical condition and there aren't many other medical options, apart from surgeries like gastric bypasses that shrink the stomach, Kumbhani said.

Qnexa isn't actually a new drug but a combination of two older medicines. One is phentermine, a drug used for short-term weight loss since the 1950s. Phentermine was half of the fen-phen drug cocktail with fenfluramine that gained popularity in the 1990s only to be banned because of complications including damaged heart valves. Qnexa's other component is topiramate, a 15-year-old drug also known as Topamax that is given to epilepsy patients who have seizures and has been linked to birth defects including cleft palates.

Each drug is supposed to help patients lose weight by tricking the body into thinking it isn't hungry. Some doctors already prescribe this combination, but Vivus would sell it in a single pill.

The FDA, which rejected Qnexa back in 2010 due to safety concerns, faces an April 17 deadline to make a ruling. An expert advisory committee voted last month to recommend the agency approve Qnexa. The FDA typically follows the advice of its expert panels but isn't bound by it.

An FDA spokeswoman didn't respond to emails requesting an interview with an official or comments on weight-loss drugs.