US cyclist Lance Armstrong has announced he will no longer fight drug charges from the US anti-doping agency, ahead of a Friday deadline.
In a statement sent to Associated Press, Armstrong, 40, says he is innocent but weary of the accusations.
His decision could lead to sanctions from the doping agency, including a lifetime ban from cycling and the loss of his tour titles.
The seven-time Tour de France winner retired from cycling in 2011.
The US Anti-Doping Agency (USADA) alleges he used banned substances as far back as 1996, including the blood-booster EPO, steroid and blood transfusions.
Armstrong sued in federal court to block the charges but lost.'Nonsense'
"There comes a point in every man's life when he has to say, 'Enough is enough.' For me, that time is now," Armstrong said in the statement.
"I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999.
"Over the past three years, I have been subjected to a two-year federal criminal investigation followed by Travis Tygart's [USADA's chief executive] unconstitutional witch hunt.
"The toll this has taken on my family, and my work for our foundation and on me leads me to where I am today - finished with this nonsense."
Armstrong had until 06:00 GMT Friday to decide whether to continue fighting the USADA charges.
The cyclist earlier accused the agency of offering "corrupt inducements" to other riders to testify against him.
The agency can impose a lifetime ban and recommend Armstrong be stripped of his titles.
Armstrong, who survived testicular cancer prior to his record-breaking Tour wins, retired after the 2005 Tour de France but made a comeback in 2009.
He retired for a second time in February 2011.
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