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Concerns have been raised about Tesla chief executive Elon Musk's behaviour in recent months.

Tesla shares have dropped sharplyafter the company's accounting chief quit after justweeks in the job and chief executive Elon Musk appeared to smoke marijuana during an interview.

In the interview streamed live on YouTube on Friday [local time], Mr Musk smoked a cigarette that the host, comedian Joe Rogan, said was a mixture of marijuana and tobacco.

"You want some, man?" Rogan asked during the lengthy two-and-a-half hour interview."You probably can't because of stockholders, right?"

"I mean, it's legal right?" said Mr Musk before taking the cigarette from Rogan and inhaling.

The interview was recorded in California where marijuana has been legalised for medical and recreational use.

In the hours of trading on Friday morning, shares in the electronic car company were down 9 per cent, falling to $US254 ($357) from their earlier high of $US302 ($424) last Friday.

The video of Mr Musk smoking marijuana came after the shock resignation of Tesla's chiefaccounting executive after just one month in the job and amid mounting concerns over thetycoon's behaviour.

In a statement to the US Securities and Exchange Commission on Friday, it was announced accounting chief Dave Morton had tendered his resignation less than a month after joining Tesla, citing concerns about the pace of the company and the level of public attention.

Mr Morton joined Tesla just days before Mr Musk announced on Twitter that he was taking the company private.

"Since I joined Tesla on August 6, the level of public attention placed on the company, aswell as the pace within the company, have exceeded my expectations," Mr Morton said in astatement.

"As a result, this caused me to reconsider my future. I want to be clear that I believestrongly in Tesla, its mission, and its future prospects, and I have no disagreements withTesla's leadership or its financial reporting."

Tesla's head of human resources, Gabrielle Toledano, also toldBloomberg Newsshe will not be rejoining the company after a leave of absence.

Tesla shares have lost one-third of their value since August and nearly a dozen topexecutives have left the company, sparking questions about Mr Musk's fitness to run bothTesla and aerospace company, SpaceX. In an interview withThe New York Timesin August, the 47-year-old detailed the "excruciating" personal toll of running Tesla.

The company has been beset by manufacturing delays and is now the subject of a federal investigation after Mr Musk announced in an August 7 tweet his plan to make the company private, sending Tesla shares soaring.

"This past year has been the most difficult and painful year of my career," he said, revealinghe often worked 120-hour weeks and his wellbeing was starting to fray.

The tweet and subsequent investigation have ignited tensions within Tesla's board,

theTimeswrote, and concerns about Mr Musk's use of the prescription anti-insomnia drug, Ambien.

"It is often a choice of no sleep or Ambien," Mr Musk said.

In the interview with Rogan, the father-of-five who has cemented himself as one of SiliconValley's most ambitious entrepreneurs, said his mind was like "a never-ending explosion"and that it was very hard to turn his brain off.

"I don't think you'd necessarily want to be me," he said. "I don't think people would like it that much."

The image of Mr Musk smoking marijuana quickly began circulating on Twitter, sparking memes based on his recent controversial comments, including calling a Thai cave diver whorescued a trapped soccer team a "pedo".