The CEO of Australia's largest listed whisky-maker quit on Wednesday after video shared with the media showed him apparently smoking methamphetamine, part of what he claimed was a years-long extortion plot.

Geoff Bainbridge said he resigned from Lark Distilling Co Ltd after learning media had obtained the content "showing me engaging in illicit drug use" years earlier, even though he had almost no memory of the events.

The Australian newspaper reported the one-minute video showed Bainbridge smoking what appeared to be a glass methamphetamine pipe while "fondling himself in skimpy black underwear".

The newspaper did not publish the video or reveal how it obtained it.

In a statement issued through his lawyer, Bainbridge confirmed it was him in the video and said it was taken overseas before he started at Lark when he attended a gathering of people he did not know.

He said he realised he was the victim of a "shakedown" after seeing the footage the next morning. Since then, he said he had been the subject of a "sophisticated, continuing and recently escalated extortion".

He said the video was shared with media after he took advice to stop responding to ongoing extortionists' threats after paying them.

"Ultimately, I put myself in a situation I shouldn't have been in. I'm a victim of extortion but that wouldn't have occurred without my poor judgement."

News of Bainbridge's departure sent the company's shares down 21% by late afternoon, hitting their lowest level since July 2021.

Bainbridge oversaw a 333% rise in the stock since joining the distiller in October 2019. He holds 5.5% of Lark, making him its third-largest shareholder, according to Refinitiv data.

In a statement, Lark said Bainbridge had left the company "to enable him to manage a personal matter".

It installed an interim managing director while the company looked for a permanent replacement.