altApril 17 - Tyler Hamilton (pictured), the 2004 Olympic champion, has tested positive for a banned substance for a second time in his career and retired, he announced today.

Hamilton won the time trial in Athens but the victory was overshadowed by accusations of blood doping.

Soon after, Hamilton 's first positive for blood doping came back, but he was allowed to keep the gold medal because his 'B' sample could not be tested.

A month later, he tested positive again.

A second doping offence is subject to a ban from eight years to life, according to the World Anti-Doping Agency (WADA) code.

Hamilton said he bought an over-the-counter homeopathic anti-depressant containing the steroid DHEA (Dehydroepiandrosterone) which is on the WADA list of banned substances.

He said: "I took a banned substance so I need to take whatever penalty they will give me and move forward.
"Today is about my leaving the sport and to talk about my depression, not the past.

"I don't want to talk about that anymore, it's about moving forward and taking care of myself.

"I'm not naive.

 "I know people will be angry with me and depression is something I need to take care of, I didn't do it at the right time or in the right way and I'm sorry for the negative spotlight."