"Taking it was something I did...to take my mind off things that were upsetting me - to make me feel better about myself," he writes in the book.

Crystal meth is a powerful stimulant that can be swallowed, snorted or injected and is extremely addictive.

Eight time Grand Slam tennis champion Andre Agassi admitted in his autobiography three years ago that he had become addicted to crystal meth in 1997 and it it sent him on "a manic apartment-cleaning binge".

Mitcham claims that the catalyst for his addiction was FINA failing to ranked him number one in the world after his victory in Beijing. 

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

Matthew Mitcham's book, Twists and Turns, tells of his addiction which he had previously kept a secret

Mitcham claimed his drug dependence was also fuelled by low self-esteem, anxiety, depression, panic attacks and repeated self-harm during his teenage years.

Mitcham, who is one of the few openly gay Olympic athletes in the world, claimed that he is now clean after seeking the help of Narcotics Anonymous and has already started looking forward to the 2014 Commonwealth Games in Glasgow. 

The Australian Olympic Committee (AOC) admitted that they had been unaware of Mitcham's problem.

"We had no idea that he had a problem - he was his usual friendly, outgoing self in London," said AOC spokesman Mike Tancred.

"He went out and supported all his teammates, was happy and chatty - the usual Matty.

"We did know that before the Games, he had a horrendous run with injuries, but we were not aware of any issues with drugs.

"But, we think that it is sad that such a talented athlete has been caught up with such a hideous drug, and we are glad to hear that he is on top of it."

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