Elon Musk says cutting back on work hours isn't an option

Skimping out on a healthy work-life balance may be the key to running a successful car company nowadays, at least in the mind of Tesla CEO Elon Musk.

“You think this is an option. It is not,” Musk wrote in a tweet in response to Arianna Huffington, who in an open letter on Friday said Musk and the future of Tesla would be better off if he regularly built in time to “refuel” and “recharge.”  Musk added that his electric car company and Ford are the only two American automakers that have avoided bankruptcy.

Musk conceded in a wide-ranging interview with The New York Times last week that he's overwhelmed by job stress, has been working up to 120 hours a week and sometimes takes Ambien to get to sleep.

Tesla has presented plenty of challenges for Musk. The company routinely loses money and is burning through cash as it ramps up development of its Model 3 sedan, a less-expensive electric car it hopes appeals to the mass market. A large number of investors known as short-sellers have bet against the company.

Musk, who recently said he might take Tesla private, has added to those pressures with lofty projections for profits and production that the automaker often fails live up to. Plus, the eccentric billionaire is the head of at least two other companies, including the rocket company SpaceX.

In her open letter, which referenced Musk's interview with the Times, Huffington urged Musk to ease up on the long hours at work.

"Working 120-hour weeks doesn't leverage your unique qualities, it wastes them," she wrote. "You can't simply power through — that's just not how our bodies and our brains work."

The Associated Press contributed to this report