As David Letterman plans to retire from a 33-year career as a late-night host, he revealed that an antidepressant saved his life.

"It saved my life," he told the New York Times. "I used to wonder how other people weren't always screaming and punching the Sheetrock. And then I started this, and I felt like, 'Ahhh, I see!' And now I don't punch Sheetrock and scream as much."

Letterman had suffered from depression for 20 years, but he was reluctant to take medication. "My friend and doctor, Louis Aronne, 20 years ago, he said, 'You should take something for this,' and I said no, because I thought it would make me loopy or make me hallucinate or make me drowsy," he told CBS' This Morning.

Letterman fought a battle with shingles, which led to him developing "nervous anxiety" along with his depression. "I was really screwed.

"I said to Louis, 'OK, OK, I'll try anything just to get rid of this depression,' he told CBS' This Morning. "Because it's different than, 'Oh, I don't feel good today.' It's different than feeling sad. It's different than feeling blue. It's really, like a friend of mine says, it's the world with 20/20 vision."

Letterman also weathered an extortion scandal in 2009 that revealed marital infidelities, and he revealed in 2013 that he sees a psychiatrist once a week.

"For a long time I thought I was a decent guy," Letterman said in an interview with Oprah Winfrey. "But yet, thinking I was a decent guy, I was still capable of behavior that wasn't coincidental to leading a decent life. That's what I'm working on. I want to really be the person I believe that I was. I wanna be a good person."

During the interview, Letterman revealed that he suffered from depression and described it as a "sinkhole" he thought he'd never escape. Medication, he said, helped him recover, and now he has compassion for others who also suffer from the condition.

"I always thought, 'Aw, you're depressed? Go do some push-ups and you'll feel better,'" he told Winfrey. "But it's not that."