Switzerland's former Olympic champion Brigitte McMahon has admitted to taking the banned blood-boosting drug EPO.
McMahon celebrates her triathlon gold medal in Sydney
The Swiss Olympic Association (SOA) confirmed on Friday that McMahon had failed an out of competition test.
The 38-year-old said she started taking small amounts of EPO in May because she was getting divorced and caring for her three small children.
She won the women's Olympic triathlon at the Sydney Games in 2000 and finished 10th in the Athens Olympics.
McMahon was in training for next year's world championships but has now been thrown off the Swiss national side.
She took the test at her home on 6 June and could now face a two-year ban.
"One of my consultants suggested I should take EPO in small doses for therapeutic reasons and said it wouldn't show up in a test," McMahon told a news conference.
"Then I made the worst possible decision and took this drug. I relied on the advice of experts, and now I don't know why," said McMahon, who holds a degree in biochemistry.
"When I was told I tested positive, I was shocked."
McMahon said it was the first time she had taken a performance-enhancing drug and was clean when she won in Sydney.