A surprise show of support for Orexigen Therapeutics Inc.'s weight-loss drug is lifting spirits of investors in a trio of obesity-drug makers and may rekindle the pharmaceutical industry's interest in the field.

Shares of Orexigen doubled on Wednesday, a day after a U.S. Food and Drug Administration panel voted 13-7 to recommend approval of its drug, Contrave, setting the stage for the first new diet pill in a decade. It followed rejections earlier this year of two obesity drugs from Vivus Inc. and Arena Pharmaceuticals Inc.

The vote is expected to clear the way for Contrave's approval to enter the market next year. The last widely used prescription diet treatment was a cocktail known as fen-phen, which was discontinued in 1997 because of concerns about heart valve damage.

It also capped a dramatic year of volatile trading in the makers of experimental weight loss drugs. Top investors such as BlackRock Institutional Trust Co. and Vanguard Group Inc. bet it cannot be long before new treatments reach the U.S. market, where two-thirds of the population is overweight or obese.

Orexigen may not be the only winner. Vivus' Qnexa also may still hit the market next year, after an initial delay, as analysts said the FDA panel's vote on Tuesday suggested the agency may not require new studies of Qnexa's heart risks until after approval.

Shares of Vivus rose 14 percent. Arena shares also rose 12 percent, although the stock remains beaten down and analysts still view the company's lorcaserin as a long-shot.

After the two earlier panel rejections this year and years of safety setbacks for obesity drugs, the Orexigen ruling may have salvaged broader investment in the area.

"If this one would have gone the other way, this would have killed any new development of any weight loss drugs," said Sven Borho, partner and portfolio manager for OrbiMed Advisors. OrbiMed held close to 5 percent of Orexigen shares as of the end of September, according to Thomson Reuters data.

The FDA is due to rule on Orexigen's Contrave by Jan. 31. Approval at that point is not a given, said Jefferies & Co. analyst Corey Davis, with the FDA potentially needing more time to develop risk-management plans and nail down post-approval commitments.

But Davis and others pointed to a 2011 approval for Contrave.

JPMorgan analyst Cory Kasimov said Contrave now had a 75 percent chance of winning approval at some point, up from his previous estimate of 45 percent. Contrave sales could reach $1.2 billion by 2018, according to BioMedTracker.

Canaccord Genuity analyst Adam Cutler said Contrave should win approval sometime in the first half of next year. Even with Wednesday's stock jump — up 103 percent in afternoon trading to $9.68 -- investors could still get Orexigen shares on the cheap, he said.

"For a drug that could be a potential blockbuster, I think the stock is still undervalued," said Cutler, who has a $19 price target on Orexigen.

A BETTER TAKEOVER TARGET

Orexigen's market value remains well below that of Vivus — about $465 million versus $730 million — even though Orexigen was the lone company of the three to win advisory committee backing for its drug.

One reason could be that Vivus is the more enticing takeover target because it does not have a big industry partner. Orexigen sold Contrave marketing rights to Japan's Takeda Pharmaceutical Co. Ltd., while another Japanese company, Eisai Co. Ltd., has rights to Arena's drug.

"The most likely potential acquirer of Orexigen would be Takeda and there probably is no rush for them to do that," Cutler said. "With Vivus not having a partner, inevitably any partnership discussions could involve M&A discussions."

Analysts said Vivus may now be able to satisfy the FDA's main concern about Qnexa: a potential increase in heart risks.

The Orexigen panel voted that the company did not need clinical studies for Contrave's heart risks before getting approval. Analysts said that stance bodes well for Vivus, if the FDA does not require such a trial for Qnexa either.

Qnexa may be more powerful at reducing weight loss. Two-year data showed patients lost 11.4 percent of their body weight, while those taking a placebo lost 2.5 percent. In four trials of Contrave, average weight loss ranged from 3.3 percent to 4.8 percent.

"There is room for several drugs, but Qnexa has impressive weight-loss numbers that really stand apart," said Needham & Co. analyst Alan Carr.

Arena's lorcaserin faces broader concerns that make approval less likely, analysts said, including potential cancer signals found in preclinical rat data.

"While there is this general improvement in sentiment around obesity, to that extent it helps Arena, but I don't think it goes beyond that," Carr said.

Of 20 analysts who follow Arena, which has a market value of about $190 million, none rate the stock a "buy," according to Starmine. Six of 10 analysts rate Orexigen "buy" or "strong buy," while seven of 15 analysts have such ratings on Vivus.

Some prominent investors appeared to have been hedging their obesity bets. BlackRock and Vanguard each were top-11 holders of all three companies as of the end of September, according to Thomson Reuters data.

The FDA's Orexigen panel ended a long losing streak for obesity drugs.

In addition to the Arena and Vivus setbacks, Abbott Laboratories' Meridia, on the market since 1997, was removed in October over concerns about heart risks.

The field was deflated by the failure of Sanofi-Aventis SA'sobesity drug

Acomplia to reach the U.S. market after a panel of experts rejected it amid fears that it may cause suicidal thoughts.

Only three drugs are in late-stage, or Phase III, development for obesity and 16 in Phase II, according to data from Thomson Reuters Pharma.

Approvals for Contrave or Qnexa could bring pharmaceutical companies back into the area, either through their own research or through more partnerships, Canaccord's Cutler said.

"In the wake of (Acomplia), I think there was a lot of concern that the regulatory bar was going to be too high and it wasn't worth the significant cost of development given the high regulatory risk," Cutler said. "If the perceived regulatory risk is lower, that equation could change."