Tokyo prosecutors arrested a former employee of Novartis Pharma K.K. on Wednesday on a charge of manipulating clinical study data for one of the firm's drugs, leading to exaggerated claims in advertising.

Nobuo Shirahashi, 63, allegedly manipulated figures for cerebral stroke incidence and other data collected by a research team at the Kyoto Prefectural University of Medicine. The falsified data led the team in 2011 to release a paper supporting the Diovan drug, which lowers blood pressure.

The arrest came after prosecutors raided the Japanese sales arm of Swiss pharmaceutical giant Novartis earlier this year over its alleged use of clinical study reports for exaggerated advertising in violation of the pharmaceutical affairs law.

As a Novartis Pharma employee, Shirahashi was responsible for analyzing data from clinical tests comparing Diovan with other drugs that reduce blood pressure. The studies were conducted at five Japanese universities between 2002 and 2004.

The Kyoto team concluded Diovan was more effective than other products in preventing stroke and angina based on the manipulated data from around 3,000 patients. The Kyoto medical school's investigative panel reported the data manipulation last year.

The Jikei University School of Medicine in Tokyo, another of the universities involved, also found manipulated data in a clinical study on the drug.

Novartis Pharma contributed a total of ¥570 million to the Kyoto Prefectural University of Medicine and the Jikei University School of Medicine between 2002 and 2012. It launched Diovan in Japan in November 2000 and achieved cumulative Diovan sales of some ¥1.2 trillion by 2012.