James Watt told the BBC claims of a "culture of fear" and "toxic attitude" were tough to hear, but said they would help make him a better chief executive.
In an open letter, signatories said a "significant number" of former staff had "suffered mental illness as a result of working at Brewdog".
In the letter, the ex-staff claimed that the firm was built around a "cult of personality" of founders Mr Watt and Martin Dickie.
The fast-growing Scottish brewer and pub chain has enjoyed rapid success and now employs 2,000 staff. But it has also courted controversy with its marketing and commercial decisions.
The letter, posted on Twitter, made a number of allegations, including a culture where staff were afraid to speak out about concerns.
It said Mr Watt and Mr Dickie had exploited publicity, "both good and bad", to further their own business goals and chased "growth, at all costs".