Qsymia is the company's only marketed product. U.S. sales of the drug started slowly, something Vivus has attributed in part to high out-of-pocket costs for patients and limited insurance coverage.
But the company said in January that prescriptions for the weight loss pill surged in late November and December. Analysts say annual sales of Qsymia will eventually top $1 billion.
Vivus shares finished at $12.88 on Thursday. Its shares have rebounded from a 52-week low of $9.86 in mid-November. They are almost 60 percent below their high of $31.21 in mid-July.