Seeking a treatment for that bane of all globe-trotting executives, the 66-year-old turned to dietary supplements widely available in Japan and the U.S., he said at a news conference in Tokyo Wednesday.
It was a package of such supplements set to be sent through the mail that brought the police to his door and could now bring down the curtain on his career. Suntory said Tuesday he resigned as police are investigating whether those supplements are illegal.
“I believe I am innocent,” said Niinami, who led the global drinks giant for more than a decade. Nonetheless, Niinami said, leaders should know better than to cause such a commotion in Japanese society. “I understand why I had to resign.”
With the global economy being reshaped by President Trump’s tariff blitz and China’s manufacturing might, Niinami’s abrupt departure from the C-suite deprives corporate Japan of one of its rarest assets: An forthright, cosmopolitan and English-speaking executive equally comfortable dispensing advice on business competitiveness to Japan’s prime minister as he is discussing climate change on global news networks.
Unlike many of his Japanese peers, Niinami was outspoken on issues ranging from sexual harassment in the workplace to the pros and cons of prodding Japanese to invest more in stocks.
In response to Trump’s tariffs, Niinami urged Japan to look for new markets and not be overreliant on the U.S. “The fundamental stance of the U.S.—prioritizing national interests over international cooperation—is unlikely to change,” he said in July in his capacity as chairman of the Japan Association of Corporate Executives, a business lobby group.
At Suntory, he stockpiled bourbon in Europe last year to prepare for the risk of an all-out trade war.
“His loss will be significant, as he was a rare voice who actively spoke out on issues during this transformative period for the Japanese economy,” said Yasuhiro Ochiai, a professor of management and information at Japan’s University of Shizuoka.
Born in Yokohama, a port close to Tokyo that was one of the first Japanese cities opened to foreign trade in the mid-19th century, Niinami studied economics at Keio University in Tokyo before completing an M.B.A. at Harvard Business School.
He spent 21 years at Mitsubishi Corp. before joining ubiquitous Japanese convenience-store chain Lawson in 2002 as president and chief executive, where he led its expansion into other markets including China and Thailand.
Niinami was the first person picked to lead Suntory from outside the ranks of its founding family in 2014, at the time a radical departure from Japanese norms.
Part of his job involved digesting the company’s acquisition of Beam Inc., the U.S. maker of bourbon whiskeys including Jim Beam and Maker’s Mark, for $16 billion, including debt. Another role was mentoring Nobuhiro Torii, a scion of the founding family who is now the company’s president.
In an emotional moment during the Suntory news conference Tuesday announcing Niinami’s resignation, Torii said of Niinami that “it is such a shame we could not continue on as partners.”
Suntory said on Tuesday that Niinami told the company in late August that police were investigating whether he purchased supplements that could be illegal in Japan. Regardless of the eventual outcome of the investigation, the board concluded his position was untenable and Niinami resigned, the company said.
In his own news conference Wednesday, Niinami laid out new details of the circumstances surrounding the probe.
He said he was in the habit of taking supplements containing CBD, a derivative of cannabis, to cope with jet lag. He said the supplements are “100% legal.”
Oils, supplements and other products containing CBD are legal in Japan—but only if they contain extremely small doses of THC, the principal psychoactive compound found in cannabis. The government tightened those rules last year, lowering the amount of THC permitted even further.
Niinami said a package containing supplements was set to be mailed to his home from elsewhere in Japan by the brother of an acquaintance in the U.S., though he knew nothing about the planned delivery. The brother’s arrest led police to Niinami.
The acquaintance had earlier mailed him a similar package, but he said he never opened it or consumed its contents because it was disposed of by his family, who have a policy of getting rid of mail from unknown senders.
“I believe that the truth will be uncovered and understood,” Niinami told reporters, saying that he doesn’t believe he did anything wrong and will cooperate with the police.
In a display of corporate loyalty typical of Japanese executives, he said he resigned to protect the brand and thanked Suntory’s employees.
“Suntory equals Japan itself,” he said.
Write to Jason Douglas at jason.douglas@wsj.com