Olympic cycling gold medallist Tyler Hamilton has been given an eight-year ban after testing positive for a banned anti-depressant in February.
The 38-year-old, who is suffering from depression, had already announced his retirement following the positive test.
United States Anti-Doping Agency head Travis Tygart said: "In cycling, eight years ineligibility for a 38-year-old athlete is effectively a lifetime ban."
Hamilton's Athens time-trial triumph in 2004 was clouded by doping allegations.
He failed a test but was allowed to keep the gold medal because his B sample could not be positively tested.
However, a month later he tested positive during the Tour of Spain and was given a two-year suspension.
Then last February, the former US Postal team rider tested positive for the steroid DHEA (Dehydroepiandrosterone) during an out-of-competition test in preparation for the Tour of California.
Hamilton, who has been fighting depression brought on by a divorce and his mother's struggle with breast cancer, admitted to taking an over-the-counter homeopathic anti-depressant containing the banned steroid and then retired in April.
USADA chief Tygart added that the ban was "an assurance that Hamilton is penalised for what would have been the remainder of his competitive cycling career".