The "Ad Astra" actor turned to the support group for 18 months after he split from wife Angelina Jolie in September 2016, reportedly following a row over his drinking, and he appreciated the fact he could expose his "ugly sides" to the other members of the all-male meetings.
He said of the group: "You had all these men sitting around being open and honest in a way I have never heard.
"It was this safe space where there was little judgment, and therefore little judgment of yourself.
"It was actually really freeing just to expose the ugly sides of yourself. There's great value in that."
The 55-year-old actor - who has six children with Angelina - admitted he had reached his limits when it came to alcohol so felt he needed to get sober.
He told the New York Times newspaper: "I had taken things as far as I could take it, so I removed my drinking privileges."
The "Once Upon a Time in Hollywood" actor - who was also previously engaged to Gwyneth Paltrow and married to Jennifer Aniston - admitted he's never felt comfortable with the scrutiny that came with fame.
He said: "In the '90s, all that attention really threw me. It was really uncomfortable for me, the cacophony of expectations and judgments. I really became a bit of a hermit and just bonged myself into oblivion...
"[My life wasn't] the lottery it appeared from the outside."
But these days, Brad has stopped worrying so much about other people's expectations.
He said: "Those dubious thoughts, the mind chatter, the rat in the skull -- that's comedy.
"It's just ridiculous that we would beat ourselves up that way. It doesn't matter. I spent too much of life wrestling with those thoughts, or being tethered to those thoughts, or caged by those thoughts."