PHILADELPHIA, Pa. ( TheStreet) -- Did a winner emerge from this week's Obesity Society meeting?

It's kind of hard to tell. The meeting, which wraps today, was a bit anti-climatic. Data presentations from the three small drug makers racing to develop new weight-loss drugs were largely in-line, offering little new information from what investors had already seen.

Perhaps Arena Pharmaceuticals ( ARNA) can lay claim to the top prize, but only because its stock dropped less -- 3% from Friday through Tuesday -- than its competitors. Orexigen Therapeutics ( OREX) shares fell 8% in the same time frame while shares of Vivus ( VVUS) lost 9%.

Vivus played a central role in what may be the only excitement to emerge from the Obesity Society meeting. The stock fell 15% Tuesday after Cowen issued a note to clients that accused Vivus of hiding the extent to which central nervous side effects of its weight-loss drug Qnexa had forced patients to withdraw from two phase III studies.

According to a Cowen analysis of data from two phase III trials presented Saturday, 2.6% and 2.1% of patients treated with full-dose Qnexa, respectively, dropped out of the studies due to cognitive side effects like "disturbance in attention" or "forgetfulness." This is compared to a placebo dropout rate of 0.8% and 0.3% in the two studies.

Cowen says Vivus didn't disclose these dropouts when the company reported top-line data from the Qnexa trials in September.

"We believe adverse events such as "disturbance in attention," "memory impairment," "amnesia," "aphasia" and "cognitive disorder" -- even if relatively rare -- will prove to be serious regulatory hurdles for a weight-loss drug. Therefore, we now have reduced conviction in the approvability of Qnexa, and partnering prospects also may be reduced," wrote Cowen analyst Ian Sanderson.

Reached on his cell phone, Vivus chief financial officer Tim Morris says Sanderson's analysis is bunk.

"The side effects of Qnexa are expected and within the profile of topiramate. They are mild and manageable and even lower than what you see on the topiramate monotherapy label," said Morris.

A bit of explanation is in order. Qnexa is made up of two currently approved drugs, combined in a proprietary formulation to promote significant weight loss. One of the drugs is phentermine, a generic weight-loss drug still available. The other drug in Qnexa is Johnson & Johnson's ( JNJ) topiramate, used to treat epilepsy and migraines.

The use of topiramate comes with well-known cognitive side effects, so the fact that some of these side effects are showing up in Qnexa patients is neither surprising nor alarming, says Morris, adding that Vivus has been particularly encouraged since the reported side event rate for Qnexa is actually lower than what you'd typically see with topiramate.

Morris said the way Cowen conducted its analysis to reach the 2.6% and 2.1% Qnexa patient drop out rates over-states the issue and is not consistent with the way the Food and Drug Administration typically analyzes safety data.

He also defended the way Vivus previously reported top-line Qnexa safety data in September as entirely proper. "We report data consistent with FDA practice and there was no intention to selectively disclose," he says.

Qnexa has demonstrated greater weight loss than either of the obesity drugs from Arena or Orexigen Therapeutics. And Vivus' stock price has outperformed its rivals in recent weeks. But if Qnexa has an Achilles heel, it's the drug's side effect and tolerability profiles.

Of course, the only opinion that matters about Qnexa's side effect profile is the one to be issued sometime next year by the FDA after it reviews the drug for approval.

Until then, expect the debate to continue.

-- Reported by Adam Feuerstein in Boston
Adam Feuerstein writes regularly for TheStreet.com. In keeping with TSC's editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet.com. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.