Tokyo prosecutors raided Novartis Pharma K.K. on Wednesday over its alleged use of exaggerated advertising for a blood pressure-lowering drug, following a criminal complaint filed by the health ministry last month.

The ministry claimed that the ads for Diovan cited clinical study reports by two Japanese universities that contained false data and concluded the drug was more effective than others in reducing the risk of cerebral stroke and angina.

Doubts over the reports surfaced in 2012, but Novartis Pharma made a rebuttal in the July 2012 edition of Japanese medical magazine Pharma Medica, a company source said.

Executives of the Japanese Society of Hypertension also endorsed the research in a roundtable discussion with experts, the source said.

In April 2012, a Kyoto University doctor questioned the credibility of the reports, saying in a post on the website of British medical journal The Lancet that it was odd to have almost similar average blood pressure in different groups of patients, the source said.

The doctor questioned the findings of a paper by a team at Jikei University School of Medicine in Tokyo. In 2013, investigators at the university found that the data on blood pressure had been manipulated.

The doctor also questioned the findings of Kyoto Prefectural University of Medicine.

The ministry's investigation panel said in a report last September that Novartis Pharma's use of the falsified reports for promotion could amount to exaggerated advertising, banned under the pharmaceutical affairs law.

Violations of the law can result in imprisonment of up to two years or fines of up to ¥2 million.

The Japanese sales arm of Swiss pharmaceutical giant Novartis contributed around ¥570 million to Kyoto Prefectural University of Medicine and Jikei University School of Medicine that conducted the clinical studies from 2002. A Novartis Pharma employee, who has since left the company, participated in the studies.