The Food and Drug Administration has closed its investigation into Mylan Inc.'s (MYL) Morgantown, W.Va., plant, finding no deficencies, following media reports that questioned its quality control.

The potential issues came to light last month in a Pittsburgh Post-Gazette report, which alleged that plant workers were overriding computer-generated warnings. Confusing statements from both the company and regulators created volatility in the generic drug maker's stock price.

Mylan shares, which were as low as $11.66 last month, jumped on the news Thursday, recently rising 3.4% to $14.06.

An FDA spokeswoman said the agency "plans no additional action." She said Mylan appeared to conduct an "adequate investigation" of the matter, with no evidence that there was any adverse impact to affected product lots.

"No data was deleted, and the audit trails were intact for each instance where the software was overridden by the operator," according to the agency's statement.

Furthermore, Mylan provided training to operators and was working to implement a software patch that would prevent employees from overriding data.

Last month, the Post-Gazette reported that Mylan had launched an internal probe to investigate whether workers at the plant had been routinely overriding computer-generated warnings about the drugs being produced at the plant. The newspaper cited an internal report and had other experts review the report and call it a significant problem.

Officials from the Post-Gazette weren't immediately available for comment.

Mylan Chief Executive Robert Coury has blasted the reporting in the article and said it contained "false, misleading and unfounded" allegations with a "biased agenda."

The FDA's conclusion, as well as Mylan's strong reaction, should ease investor concerns.

"The fact management squashed these shocking allegations so quickly dissolves any credibility doubts and puts the focus back where it belongs," Natixis Bleichroeder analyst Corey Davis said, stressing Mylan's recent second-quarter earnings report and 2009 projections.

-Thomas Gryta; Dow Jones Newswires; 212-416-2169; thomas.gryta@dowjones.com