BOSTON ( TheStreet) -- Investors craving more action from obesity drug stocks have another catalyst looming within the next 10 days and a full calendar through the end of the year.

Vivus ( VVUS) is expected to announce top-line results from a follow-up study of its weight-loss drug combination Qnexa before the end of September. This study will provide two-year safety and efficacy data on Qnexa and possibly address one of the major shortcomings that compelled a U.S. advisory panel to vote against Qnexa in July.

Short sellers and skeptics of the current crop of experimental obesity drugs have had held the upper hand so far. Vivus shares tanked after the Qnexa setback in July. Last Thursday another negative vote by a U.S. advisory panel reviewing Arena Pharmaceuticals' ( ARNA) weight-loss drug lorcaserin caused that stock's value to also fall precipitously.

That leaves Orexigen Therapeutics ( OREX) as the next potential winner -- or victim -- depending on your point of view. Orexigen will bring its obesity drug Contrave in front of a yet another U.S. advisory panel on Dec. 7.

Vivus shares are down about 50% to $6 since the July panel vote. Arena shares, at $1.88, have lost more than 70% of their value in the past week. Orexigen, with the last obesity drug standing, has seen the value of its stock rise about 30% to $6 in the past week.

Before the Contrave panel, the U.S. Food and Drug Administration will issue approval decisions for lorcaserin on Oct. 22 and Qnexa on Oct. 28. The two decisive and negative advisory panel votes make it more likely that FDA will decide not to approve either drug at this time since the agency usually goes along with the recommendations of its advisory panels.

Vivus hopes to counteract the perception that Qnexa may not be safe enough for approval with two-year data from a double blind, randomized extension study known as "Sequel."

Patients in the Sequel study continued receiving the same treatment (either Qnexa or placebo) that they were receiving in a previous one-year phase III study. The goal of the Sequel study, which enrolled about 650 patients, is to measure the weight-loss efficacy and safety of Qnexa compared to placebo in patients treated over two years.

The lack of two-year data to assess Qnexa's longer-term safety was a significant sticking point with members of the FDA advisory panel who reviewed the drug in July.

Particular attention will be paid to the side effect profile of the high dose of Qnexa from the Sequel study, since this dose was where most of the worrisome side effects of the drug occurred.

If the Sequel results are positive, Vivus could submit the two-year Qnexa data to FDA for review. However, it's not clear if the agency would have time to review the data by the agency's Oct. 28 deadline. If not, FDA could extend the Qnexa review by another three or six months.

Key, upcoming events in the race to develop an approvable obesity drug:

Before end of September:

Top-line results from Vivus' two-year "Sequel" extension study of Qnexa.

Oct. 22:

FDA approval decision date for Arena Pharmaceuticals' lorcaserin.

Oct. 28:

FDA approval decision date for Vivus' Qnexa.

Dec. 7:

FDA advisory panel for Orexigen Therapeutics' Contrave.

Before end of 2010:

Arena reports results from phase III study of lorcaserin in obese patients with diabetes -- the so-called Bloom-DM study.

Jan. 31, 2011:

FDA approval decision date for Orexigen's Contrave.

--Written by Adam Feuerstein in Boston.

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