QVT Financial, the third-largest shareholder in obesity drugmaker Vivus, intends to vote for the full slate of nine directors proposed by dissident investor First Manhattan, a source familiar with QVT's thinking said on Wednesday.

The investment firm, which owns a roughly 8.3% stake in Vivus, according to its latest public filings, has come to the decision because it believes that changes are needed at the drugmaker, the source said. First Manhattan, Vivus' largest shareholder with a 9.9% stake, is seeking to take full control of the company's board with its own nine nominees. Vivus holds its annual meeting of shareholders July 15.

The source asked not to be named because he was not authorized to speak with the media. QVT declined to comment.

Representatives of Vivus and First Manhattan could not be immediately reached for comment. First Manhattan has criticized Vivus for the disappointing sales of its diet drug Qsymia. The investor has also proposed a new chief executive, former AstraZeneca senior executive Anthony Zook.

First Manhattan has said that Vivus' board and management mishandled the launch of "the best obesity drug ever developed" by not seeking the commercial muscle of a bigger pharmaceutical company to address the large U.S. weight-loss market. Vivus has maintained that a full overhaul of its board and a new management would delay or jeopardize discussions with potential commercial partners for Qsymia, hindering the drug's success.