Shares of Vivus Inc. more than doubled early Thursday after a U.S. FDA advisory panel recommended the agency approve the company's new weight-loss drug Qnexa.

Vivus jumped $9.45 to $20, leading other diet-drug developers such as Arena Pharmaceuticals and Orexigen Therapeutics higher. Qnexa is one of three drugs competing for the first U.S. approval of a prescription weight-loss drug since Roche's Xenical in 1999.

Data so far indicates the drug is the most effective in helping patients lose up to 10 percent of their body weight, ABC News said.

The FDA isn't required to follow the panel's recommendations, although it generally does. An official approval or a rejection of Qnexa is expected by April 17. The panel voted 20-2 vote for approval, saying Qnexa's benefits for the chronically obese outweighed potential risks the drug may pose, according to ABC News.

Qnexa was presented before the advisory panel in 2010, but it recommended against the drug 10-6 before the FDA rejected it for further testing, according to The New York Times.

Here are some things to know about Qnexa.

Meaningful Efficacy Benefit

There is an urgent need for better pharmacologic options for individual patients, Elaine H. Morrato, an assistant professor at the University of Colorado, Denver, told The NYTimes.

I believe that Qnexa demonstrated a meaningful efficacy benefit and that there are consequences to nontreatment of obesity, she said. Morrato voted against the drug in 2010 but voted in approval of it on Wednesday.

Qnexa is a combination of two drugs - phentermine, which is a stimulant, and topiramate, an epilepsy and migraine drug - also known by the name Topamax.

The Times reported that use of Qnexa led to an average weight loss of approximately 10 percent body weight after one year. However, some of that lost weight was gained back in the second year of use.

Qnexa also reportedly helped lower both blood pressure and blood sugar, improving users quality of life.

Vivus is expected to market Qnexa to those who meet the government's obesity standards, which is calculated at a body-mass index of 30 or greater. The labeling will include instructions stating that those who lose less than three percent of their body weight in three months should stop taking the drug, reported WebMD.

One-third of Americans are obese. This has been linked to high blood pressure, diabetes and other serious health problems. It has also saddled the healthcare industry with billions of dollars in healthcare treatment.

Heart Risks Concerns

However, not everyone believes the drug is ready for market.

The consequence of making a mistake here is huge, cardiologist Michael Lauer, who was one of two panel members who voted against Qnexa, told The NYTimes. We've unfortunately had many examples of having made mistakes before.

Side effects of Qnexa include increased heart rate, heart attacks and arrhythmias, according to ABC News. Critics believe these risks are too substantial to allow Qnexa to hit the market, especially since the long-term effects are unknown.

Public health cannot tolerate another diet drug approved that has not been accepted for cardiovascular risk especially in light of the suggested findings of Qnexa, Sidney Wolfe, director of the health research group at advocacy group Public Citizen, told ABC News.

Pregnant women are particularly at risk. Clinical trials revealed potential concerns over birth defects in babies whose mothers took Qnexa during pregnancy.

Topiramate, or Topamax, one of the two drugs in Qnexa, has been linked to the risk of cleft lip and palate in babies whose mothers took the drug while pregnant, according to WebMd.

Vivus has said it will formulate a plan to make sure pregnant women do not take the drug.