Mickey Grimes has apologised after being stripped of his Pan Am Games 100m title for testing positive for ephedrine.
Grimes won 100m individual and relay gold
The American is the second athlete in as many days to be punished after Surinam's Letitia Vriesde tested positive for caffeine and lost the 800m gold medal.
Grimes, who failed to make the US championships final, won last Wednesday's race in a time of 10.10 seconds.
The gold medal will now go to Jamaica's Michael Frates with American Marcelle Scales stepping up to silver and Anson Henry of Canada taking bronze.
Grimes was also deprived, along with the rest of the US team, of the 4x100m relay gold.
"I understand athletes need to take responsibility for everything we put in our bodies," said Grimes in a statement released by the US Olympic Committee (USOC).
"I made a mistake and I know that my action carries with it a penalty. I sincerely regret letting down the US delegation and my country, and I look forward to representing the United States in the future."
USA Track and Field added: "We have spoken to Mickey, and we feel assured he had no intention of gaining any competitive advantage.
"Mickey is one of our top young athletes, and he has learned an important and difficult lesson from this."
America's disqualification from the relay means Brazil now take gold with silver going to Trinidad and Tobago and Cuba getting the bronze.
Vriesde, the 1995 silver medallist, had such a high level of caffeine in her system that it provoked the Pan Am Games president Mario Vasquez Rana into a withering attack.
"She would have needed to drink five gallons of coffee for that level of caffeine to be found in her body," he said.
"Over 400 controles have already been taken of the 900 we'll be performing up to 17 August."
The tests are being carried out at an anti-doping laboratory in Montreal.
Germany's European 400m relay
champion Florence Ekpo-Umoh has been banned for two years by the
German athletics federation after testing positive for banned
The Nigerian-born athlete was tested in South Africa on 24 January and her urine sample showed the presence of Stanozolol.
The athlete, who claimed that the urine sample analysed did not
belong to her, will be due to return to competition on 10 March,