Four years earlier he had triumphed at Beijing, winning gold with the greatest single platform dive in Olympic history. Now, not even in the top 12, he sat sobbing in defeat.

What the millions watching didn't realise was that behind his devastating loss in London lay a victory of a different kind.

For Mitcham had made it to the 2012 Olympics only after beating a secret methamphetamine addiction in 2011 that had almost derailed his career, and his life.

In a book to be released on Monday, Twists and Turns, Mitcham unveils his battle with low self-esteem, anxiety and depression, punctuated by panic attacks and repeated self-harm as a teenager, which helped precipitate his dependence on crystal meth.

Following on the heels of fellow Olympian Ian Thorpe's revelations about battles with the black dog, it's yet another sobering reminder of the price top athletes pay for their place in the sporting firmament.

''The psychological support of athletes is underdone,'' warns Jeff Bond, a former head of sports psychology at the Australian Institute of Sport, who believes sporting bureaucracies need to give the issue far greater prominence.

''I think it's the key issue [for top athletes] and the issue that has probably least funding and emphasis in professional and Olympic sport.''

Mitcham's at times searingly frank memoir makes clear that some of his problems went back to childhood.

His single mother, Vivienne, was a loving but emotionally erratic parent, diagnosed years later with Asperger's syndrome. As a child, he was terrified of her moods and took solace in books and a rusty trampoline bequeathed to the family second hand. Hours of jumping bred an ability to show off spectacularly at the local pool, which is where he was spotted by the Australian Institute of Sport.

Forced to choose between competitive trampolining and the more clinical world of diving, Mitcham chose the latter.

It was, he writes, ''my only ticket to being special''.

But the rigours of training and problems with diving authorities drove him increasingly towards clubbing, binge drinking and recreational drugs at weekends. In 2006 he quit the sport altogether.

A new and more sympathetic coach, Chava Sobrino, coaxed him back into competition six months later and the Beijing gold miraculously followed.

But even that triumph didn't satisfy Mitcham's inner perfectionist. The FINA ranking system still had him at only world No. 2.

''I had still failed to achieve my childhood dream of becoming the best in the world at something,'' he writes.

Self-doubt came crashing back, fuelled by injury. Secretly smoking crystal meth to boost his moods, he was soon in the grip of addiction.

He knew the drug's dangers. But ''taking it was something I did … to take my mind off things that were upsetting me - to make me feel better about myself.''

The openly gay Mitcham has climbed back from last year's depths with the aid of Narcotics Anonymous, a drug rehabilitation clinic, hypnotherapy and the support of his inner circle. He's chased the demons away and is training for the Commonwealth Games in Glasgow.

In therapy still, he believes he is happier and healthier. As for fully understanding himself, he writes: ''The answers continue to elude me. I may work it out one day.''