Qnexa diet pills won the backing of a federal advisory panel Wednesday, but still require approval from the Food and Drug Administration before the weight-loss pills reach store shelves.

The 20-2 vote of confidence from the nonbinding panel paves the way for FDA officials to approve an anti-obesity prescription drug for the first time since 1999.

A decision on Qnexa's approval is expected in April.

FDA officials originally rejected Qnexa in 2010 because of concerns that the drug caused heart defects, psychiatric problems and birth defects. An FDA expert on birth defects estimated that mothers who took the drug would cause five in 1,000 births to result in babies with cleft lips, according to The Associated Press. That rate is nearly 10 times the average rate of cleft palates in babies, according to statistics from the National Institute of Dental and Craniofacial Research.

Vivus, maker of Qnexa, resubmitted the drug and included additional safety information in 2011.

For the two-thirds of Americans considered overweight, the drug could offer an alternative or supplemental method to weight loss.

Numerous drugs makers tried to enter the diet pill market only to be rebuked by the FDA over side effects.

One of the best known examples is fen-phen. A combination of two weight-loss drugs, fen-phen was successful at curbing appetite and helping patients lose weight. Several patients showed significant side effects, the most serious being heart problems.

A 30-year-old woman developed heart problems a month after beginning a fen-phen regimen and died a few months later. As similar reports began to roll in, the FDA requested that fen-phen be removed from the market in September 1997.

Lawsuits filed against the maker of fenfluramine, one of the components of fen-phen cost the drug maker American Home Products, now known as Wyeth, an estimated $14 billion.

Qnexa also contains phentermine, the other component of fen-phen.

Since regulators removed fen-phen from the market, many drug makers tried to fill the gap.

Regulators rejected anti-obesity drugs Acomplia and Taranabant due to psychiatric side effects including depression and suicidal thoughts. The FDA also prohibited Reductil, which researchers showed caused heart attacks and strokes.

The only anti-obesity medicine currently approved by the FDA is Orlistat, sold over-the-counter as Alli. Orlistat is effective, but its results are moderate. Users can expect to lose 6 pounds per year and have to contend with side effects such as loose, oily stool, according to a 2009 study published in The Cochrane Library.

Backing by a federal advisory panel bodes well for Qnexa, but doesn't make its approval a slam dunk. In 2010, a panel backed anti-obesity drug Contrave by a vote of 13-7. The FDA however went against the panel's advice and asked the drug maker for more information about potential side effects.