Hamburg  - Olympic cycling champion Tyler Hamilton of the United States retired on Friday after admitting to have failed another doping test.

Hamilton, 38, told the cyclingnews website that he tested positive for the steroid dehydroepiandrosterone (DHEA) at an out-of-competition test in February.

Hamilton said he was aware that an over-the-counter medication he used to treat depression contained the banned substance. He said he used the medication after his mother was diagnosed with cancer.

"What I did was wrong and yes, I did know it (DHEA) was on the list of banned substances. I also knew that USADA could have shown up any day and at any time to test me.

"But, I was going through a very rough moment and I was desperate. I heard about it and I thought I would try it out as an act of desperation," said Hamilton.

The 2004 Olympic champion faces a ban of at least eight years, but more likely a life ban, over the latest offence. As a result, he retired.

Hamilton was caught using illegal blood transfusions at the 2004 Vuelta of Spain, a month after his Olympic gold, and banned for two years. He also tested positive for the same offence at the Olympics but could keep his gold because the b-sample could not be analysed due to inappropriate storage.

Hamilton was also linked with doping in the Spanish probe centring on doctor Eufemiano Fuentes, whom he allegedly paid more than 50,000 dollars for various doping substances and methods. He was suspended by the Tinkoff team over these allegations.

The former lieutenant of seven-times Tour de France winner Lance Armstrong last rode for the American Rock Racing team he joined in 2008. (dpa)