Vivus shares rose as much as 16 percent to $7.34 on Monday morning on Nasdaq, while Orexigen shares touched a high of $3.52, gaining more than 22 percent. By noon they were trading at $6.82 and $3.33, respectively.
Vivus and Orexigen are among several drugmakers vying to market the first new prescription diet drug in more than a decade. Both of their drug candidates had been denied marketing approval by the U.S. Food and Drug Administration on heart safety concerns, among others.
Mountain View, California-based Vivus said two-year data from a trial of its weight loss Qnexa drug showed that it helped reduce blood pressure levels and let patients cut down on the use of anti-hypertensive medications by as much as 19 percent.
JP Morgan analyst Cory Kasimov said the new set of data were not a "big surprise" but reinforced the drug's efficacy.
Most analysts expect the ultimate decision on the drug to come down to concerns related to birth-defect risks and not on heart-safety issues.
"This benefit that you see, it is not due to the drug. It's a natural thing that happens to you when you lose weight. All this does not reduce the concern over birth defect," Brean Murray, Carret & Co analyst Jonathan Aschoff, who remained skeptical on the Qnexa's appovabality said.
In January, the FDA asked for more information about birth defects involving a component of Vivus's drug in offspring of women treated with the drug.
Vivus said it will update on its plans for child-defects analysis by the end of this month, which will be more closely-followed for the drug's approval.
Separately, Orexigen Therapeutics Inc (OREX.O), which is also developing its diet pill Contrave, said the drug helped obese patients to maintain normal 24-hour Circadian patterns over a year of treatment.
Vivus said the latest study showed patients treated with a top dose of their drug sustained weight loss of greater than 10 percent over two years, which led to clinically relevant reductions in blood pressure and increase in high-density lipoprotein levels.
Needham & Co analyst Alan Carr said the latest trial data supported Qnexa's cardiovascular benefits in the long-term and confirms the drug's weight-loss benefits over its competitors.