In a new book titled Twists and Turns, which will be released on Monday, Mitcham confesses to taking methamphetamines.
The 24-year-old claims to have taken drugs after struggling to come to terms with his number two world ranking, despite winning gold in the 10-metre platform diving event at the 2008 Beijing Olympics.
"I had still failed to achieve my childhood dream of becoming the best in the world at something," Mitcham said.
Mitcham, who lost his title as he finished 13th at the London Olympics this year, said he turned to crystal meth in the hope of boosting his fading state of mind.
"Taking it was something I did ... to take my mind off things that were upsetting me - to make me feel better about myself," he said.
The autobiography also includes admissions of binge drinking and recreational drug use as he battled depression, anxiety and low self-esteem.
And once he started, Mitcham said he struggled to take himself off the substances.
"Nobody suspected anything," Mitcham said in a quote from The Age.
"I'd done such a good job of hiding it and maintaining my functionality, but it scared the s*** out of me that I didn't have control.
"I'd always said to myself, 'I'll stop as soon as I want to'. And as soon as I wanted to, it wasn't that easy. That was terrifying. And it was getting closer and closer to the Olympics.
"People kept remarking on how they were surprised that a gold medal and fame hadn't changed me," Mitcham added.
"I always responded 'Why would I change? Being me is the easiest person to be'.
"I was lying. It wasn't."
Mitcham's revelations come after Australian swimming great Ian Thorpe also detailed a battle with alcohol addiction and depression in a book released last month.