"Whether any drug will become another Fen-phen is hard to predict," said Dr. Gerard Mullin, associate professor of medicine at the Johns Hopkins School of Medicine. "Every time we see a drug recalled, none were predictable, but it seems that similar classes of drugs can have inherent problems."
It's also unclear to some experts whether topiramate actually works.
"The anticonvulsant in both Contrave and Qnexa is a new variation on the theme of tweaking brain pathways to adjust appetite, but does not appear to be more than a minor innovation to me, and one of questionable utility," said Dr. David L. Katz, associate professor adjunct in public health practice at the Yale School of Public Health.
"We did very detailed studies and found it wasn't the phentermine. It was fenfluramine that was linked to the heart issues," Katz said.
Fujioka said the trials for Qnexa, Lorcaserin and Contrave lasted about a year. The drugs were tested on about 4,500 patients each.
However, others believe there have not been enough studies done to show that these drugs are safe for most patients.
"Just because these compounds don't have the same chemical mix as Fen-phen doesn't mean they don't have a chemical mix that can cause long-term harm," said Joanne P. Ikeda, nutritionist emeritus and former co-director of the Center on Weight and Health at the University of California, Berkeley. "I think we should demand long-term (three- to five-year) safety studies for these drugs."
Keith Ayoob, director of the nutrition clinic at the Rose R. Kennedy Center at the Albert Einstein College of Medicine, agreed.
"The new drugs seem safe, but so did the Fen-phen combo," he said.
Many experts, including Ayoob, said it is safe to assume that there will be side effects with these drugs.
"It is difficult to believe the risk of memory loss and other neurological effects found with topimarate will provide adequate safe use," said Dr. George L. Blackburn, associate director of nutrition at Harvard Medical School.
Blackburn said if the drugs do end up on the market, they will target those who are obese and possibly morbidly obese.
"Studies have looked at the morbidly obese -- about 7 percent of our population falls into this category -- that's a group that has a huge need," said Fujioka.
Though risky, invasive procedures such as gastric bypass surgery clearly offer better results than taking diet pills. But many obese Americans may not qualify for surgery. And given the grim history of many diet pills that have come and gone, many experts said they don't think the answer to the obesity epidemic can be found in a pill.
"Weight loss drugs have a checkered history with regard to cardiovascular risks," said panelist Dr. Sanjay Kaul, a cardiologist at Cedar Sinai Medical Center in Los Angeles. "We don't have enough evidence here to evaluate cardiovascular risk other than increased heart rate."
Eric Coleman, deputy director of the FDA division that oversees metabolic drugs, said he was surprised by the vote.
"I was a little surprised the vote went as it did, but you learn in an advisory committee that you never know which way it is going to go."
Coleman said it was clear a lot of panelists weren't strongly against the drug but just had "lingering concerns to make them vote no."