The German chief executive of major Japanese optical equipment maker Olympus has resigned after allegedly purchasing illegal drugs, the company announced Monday.

Stefan Kaufmann became CEO in April 2023, having been a member of the board of directors since 2019. He first joined the European branch of Olympus in 2003.

Olympus shares plunged 6% in morning trading as the company apologized in a statement “for the concern this has caused our shareholders, customers and all stakeholders.”

“After receiving an allegation that Mr. Stefan Kaufmann had purchased illegal drugs, Olympus, in consultation with external legal counsel, immediately investigated the facts, made a report to the investigating authorities and cooperated fully to their investigation,” the statement said.

The company’s board of directors then “unanimously determined” that Kaufmann “likely engaged in behavior inconsistent with our global code of conduct.”