Olympic champion Tyler Hamilton, once touted as the next great American cyclist and an heir to Lance Armstrong's throne atop the sport, ended his doping-tarnished career Friday by saying he tested positive for a banned substance and would retire.

Hamilton admitted taking an herbal product for two days in February to combat depression, knowing it included a steroid.

"There's nothing to fight about," the 38-year-old Hamilton told The Associated Press. "I took a banned substance. I accept the consequences. You make mistakes in your life and I accept the penalty like a man."

Hamilton will likely receive a ban from the U.S. Anti-Doping Agency that may range from eight years to life, a sentence that would have ended his racing days anyway.

"He has had a cloud over his career for a while now and the sport is better off without him," said Pat McQuaid, president of the International Cycling Union.

Hamilton's win at the 2004 Athens Games was overshadowed by a blood doping scandal. He tested positive for doping a second time later that year, served a two-year suspension and returned to racing early in 2007 — never revealing that he was fighting depression, which he said runs in his family.

Going through a divorce and seeing his mother fight breast cancer made things worse in recent months, Hamilton said.

Seeking relief, he took something called Mitamins Advanced Formula, billed as a "natural depression treatment with vitamins, herbs and supplements."

"Obviously, that was a mistake," Hamilton said.

In a statement, USADA said it will continue going through the process of issuing a sanction.

"Although Mr. Hamilton has now retired from the sport of cycling and has publicly accepted responsibility, this is a pending matter and USADA will make an announcement of the final outcome and imposition of the exact sanction in accordance with the rules when the process is complete, which should be in the coming months," the statement said.

The Mitamins product contains common things such as vitamins D, B-6 and B-12, along with thiamin, riboflavin and calcium. Each serving also contains 20 milligrams of a steroid called Dehydroepiandrosterone — DHEA, as it's known.

"Clinical research has suggested that taking DHEA orally might improve the symptoms of depression," reads the company's Web site.

Hamilton said the amount of the steroid found in his system was "so, so low" and that subsequent tests, including ones later that same week before the Tour of California, all came back negative.

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

Hamilton said he was taking a prescription antidepressant called Celexa, and was feeling so badly a few months ago that he decided to double up on the dosage. After seeing no significant change in his mental state, Hamilton stopped taking the drug entirely.

He tried the Mitamins product, he said, on Feb. 6 and 7. USADA testers knocked on his door the next day.

"I was thinking everything would be fine," Hamilton said. "It might sound a little crazy, but I wasn't really worried. I wasn't really stressing about it. Maybe it's because of everything else I was going through. I don't know why."

About five weeks later, he learned everything was not fine.

Citing bronchitis, Hamilton did not ride in the Vuelta of Castilla and Leon in Spain — the race where Armstrong fell and broke his collarbone. And he was expected to be the leader of Rock Racing's team for a race in Portugal earlier this month, but was replaced on the roster shortly before that event.

At the time, few knew why.

"This is, for me personally, a really tough day," said Rock Racing owner Michael Ball. "My personality is to always fight for what I feel is right."

Others around Hamilton also encouraged him to fight the latest positive test. Hamilton's attorney, Chris Manderson, said they were mapping "several different strategies" including one to file a federal suit against USADA over the testing.

"Tyler has decided he does not want to pursue that route," Manderson said. "He wants to focus on the reasons why he did what he did and he wants to focus on getting better and getting on with his life."

Hamilton won the road time trial at the Athens Olympics, capping one of the finest days USA Cycling had known.

Americans won three medals that day on a road along the Saronic Gulf, with Hamilton's gold and Bobby Julich taking the bronze in the time trial and Dede Barry winning silver in the women's time trial.

Soon after, Hamilton's first positive test for blood doping came back, but he was ultimately allowed to keep the gold medal because his 'B' sample collected in Athens could not be properly tested. A month later, he tested positive again.

Hamilton has long denied participating in blood doping, the transfusion of extra blood that can increase endurance because more red blood cells are available to deliver oxygen to muscles.

For this latest positive test, he denied nothing.

"I knew it was banned," Hamilton said.

Hamilton briefly considered himself retired last year, then returned to compete in several races, plus won USA Cycling's road race national championship by less than one one-hundreth of a second.

He doesn't know what he'll do next, other than focusing on his health and family.

"This isn't about a test. It's a bigger issue," Hamilton said. "It's a disease that I'm going through, that my family has gone through, that I need to take care of. Cycling is just a sport, racing your bike from Point A to Point B. What I'm going through is so much bigger."