The actor revealed his struggles in a 2006 interview with 60 Minutes. "I went [to rehab], I got sober when I was 22 years old," Hoffman said. "You get panicked ... and I got panicked for my life."
Hoffman, who sought treatment after graduating from New York University's Tisch School of the Arts, also talked about the importance of getting treatment early in his career.
"I have so much empathy for these young actors that are 19 and all of a sudden they're beautiful and famous and rich," he said. "I'm like, 'Oh my God, I'd be dead.' I think back at that time and I think if I had the money, that kind of money."
After staying clean for 23 years, Hoffman relapsed and entered rehab last May. He told TMZ his setback came in 2012 after he started abusing prescription drugs and then moved on to snorting heroin.
Actress Kristen Johnston, Hoffman's former college classmate and a longtime friend, was one of the few privy to the actor's battle with addiction.
"Sadly, after being sober for years & years, he relapsed & has been grappling with his addiction for last few yrs.," she Tweeted, noting that Hoffman's love of his family, his career and friends weren't enough to overcome the power of addiction.
"I feel that part of the problem might have been his shyness & his deep need for privacy, which prevented him from being able to be open with others about it," she wrote. "Whatever the reason, his brilliant work will live on."