Shares of obesity drug developers Vivus Inc. and Orexigen Therapeutics Inc. rose Monday as regulators prepared to announce their decision on Vivus' experimental drug Qnexa.

The Food and Drug Administration is scheduled to publish its decision on Qnexa by Tuesday. A panel of FDA advisers recommended in February that the drug be approved. The agency is not required to follow the advice of its panels, but the 20-2 vote was a strong endorsement for Qnexa.

The FDA initially refused to approve the drug in 2010 over concerns that it can cause heart palpitations and birth defects if taken by pregnant women.

The FDA approved a competing drug, Belviq, in late June. Arena Pharmaceuticals Inc. and its partner Takeda Pharmaceuticals plan to start selling Belviq in early 2013. Orexigen is still running clinical trials of its product, Contrave, and it expects to ask for marketing approval in 2014.

Qnexa is generally seen as the most promising of the three drugs because patients who took it lost the most weight. Qnexa combines two older drugs: the amphetamine phentermine, which is approved for short-term weight loss because it helps suppress appetite, and topiramate, which is believed to make patients feel more satiated. Topiramate is marketed as Topamax, an anti-seizure drug, by Johnson & Johnson.

Belviq was the first new long-term weight loss drug approved in more than a decade.

Shares of Vivus rose $1.55, or 5.7 percent, to $28.70 on Monday. Orexigen shares gained 34 cents, or 4.8 percent, to $7.40, while Arena Pharmaceuticals shares declined 7 cents to $11.11.