As far as lorcaserin is concerned, the study results indicated the drug improved cardiovascular risk factors such as cholesterol and triglycerides, as well as quality of life factors such as physical function, self esteem and sexual enjoyment. The company now believes the data leaves Arena on track to file for regulatory approval late this year. And according to Reuters, Arena CEO Jack Lief said the company is in discussions with potential partners.

this study adds to earlier findings that 47.2 percent of subjects taking lorcaserin twice a day achieved at least a 5 percent reduction in weight — a key threshold — after a year. only 25 percent of patients who took a placebo achieved the same weight loss. The study involved 4,008 patients.

more specifically, of those who completed the treatment, 63.2 percent lost at least 5 percent of their weight, compared to 34.9 percent of patients on a placebo. And 35.1 percent of these lorcaserin patients lost at least 10 percent of their weight, compared to 16.1 percent for placebo.

Obesity is one of the nation’s most serious public health problems. According to the National Institutes of Health, 65 percent of U.S. adults are overweight or obese. The economic costs associated with obesity are significant, too, with the nation’s annual medical burden from the condition estimated at $147 billion in 2008, according to a recent report in Health Affairs.

Unquestionably, the market for diet drugs could be very large, which is why analysts believe there may be room for all three companies: Arena, Vivus and Orexigen. Since a 5 percent to 10 percent decrease in weight can be medically significant, there’s bound to be demand for the drugs. What’s more, each drug is designed to appeal to a specific group of patients.

The drugs belonging to Arena’s rivals achieved better weight-loss results. For example, Vivus’ Qnexa reduced patients’ weight by up to 14.7 percent (with the full dose), on average.

Arena is differentiating itself by trying to position lorcaserin as the safest of the drugs. While the other two drugs use phentermine which is know to increase blood pressure, Arena’s drugs sometimes even decreased it, as Lief told Xconomy’s Luke Timmerman.

Of course, all three experimental drugs will have to overcome the lingering stigma of Wyeth’s (WYE) fen-phen diet pill fiasco when officials linked the drug to heart-valve damage. Other attempts to develop such a drug by Sanofi Aventis (SNY), Pfizer (PFE) and Merck (MRK) failed because the candidates had serious side effects.

Lorcaserin is a new drug that actually works in a way similar to fenfluramine, part of the fen-phen combo, but is much more selective in the receptors it affects. The company said lorcaserin was not associated with heart-valve problems. It is designed to block appetite signals in the brain by stimulating the serotonin 2C receptor.

Arena said its trial found that lorcaserin helped reduce patients’ cardiovascular risk factors without increasing blood pressure or heart rate. as for the side effects, the most common ones were headache, nausea and fatigue.

Vivus’ drug is also a combo therapy that mixes the other generic drug in the fen-phen combo, phentermine, with the generic topiramate, sold as Topamax by Johnson & Johnson (JNJ ). The latter is known to have cognitive side effects such as diminished memory and concentration, which a Cowen analyst Tuesday said Vivus was hiding. Vivus, according to TheStreet.com denies it. Orexigen has two candidates, Contrave, which also mixes two generics and is in late-stage studies, and Empatic, in middle-stage trials.

Orexigen also released drug trial data for Contrave on Tuesday. The data showed that approximately 25 percent to 33 percent of patients lost 10 percent or more of their body weight and 12 percent to 16 percent lost at least 15 percent. Orexigen might also market its drug as reducing blood sugar levels.

For now, it seems that Vivus’ drug wins in the weight-loss department. meanwhile, if you ask Arena, it will say its drug’s safety profile is the best. perhaps there could be room for other, less aggressive, treatments in the market, depending on the patient. The pressure’s on, though. at least half a dozen other companies are also in earlier stages of developing weight-loss drugs.