LAUSANNE, Switzerland — The World Anti-Doping Agency on Thursday asked the sport's highest court to ban U.S. cyclist Tyler Hamilton for life for doping.

The former Olympic champion accepted an eight-year ban from the U.S. Anti-Doping Agency last month after he admitted taking a steroid in an herbal remedy for depression.

It was the 38-year-old Hamilton's second doping offense, which usually triggers a lifetime ban, and he said he would retire.

The Court of Arbitration for Sport said Thursday that WADA had challenged the American ruling.

"WADA requests that the resolution signed June 11 be set aside and that a lifetime period of ineligibility be imposed on Hamilton," the court said in a statement.

Hamilton tested positive for the steroid known as DHEA in an out-of-competition sample taken in February.

He later told The Associated Press he took the remedy because he was going through a divorce and his mother was fighting breast cancer.

"I took it to help my mental state," Hamilton said in April. "I did not, 100 percent, take it for any performance enhancement."

Hamilton said he would retire from cycling rather than fight the case. A CAS ruling on WADA's appeal is expected within four months.

He previously served a two-year ban for blood doping, which ended in 2007, after being caught within months of becoming the Olympic time trial champion.

That gold-medal performance at the 2004 Athens Games also was clouded by suspicions of blood doping, but problems at the laboratory meant his backup 'B' sample could not be tested.

Hamilton returned to professional cycling after his first ban with the U.S.-based Rock Racing team. He was national road race champion last year.