Ukrainian javelin thrower Oleksandr Pyatnytsya has been stripped of his silver medal from the 2012 Olympics by the International Olympic Committee after a retest of his sample exposed an illicit substance.
The IOC says the steroid turinabol was found in the retest and that its disciplinary committee imposed the sanction.
Antti Ruuskanen of Finland now moves up to silver and Czech Vitezslav Vesely up to bronze from fourth. The gold was won by Trinidad and Tobago thrower Keshorn Walcott.
The IOC also said that three other athletes were caught in retests of samples from Beijing 2008 and London 2012, none of them medallists.
They are weightlifters Nurcan Taylan of Turkey and Hripsime Khurshudyan of Armenia, and Belarus hammer thrower Pavel Kryvitksi.
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The IOC has conducted a series of retests with new scientific methods as it stores Olympic samples for 10 years.
In total, 98 athletes have tested positive in two rounds of retests from the two Games in which 1243 samples were examined.
The 840 Beijing retests saw 60 adverse findings (23 medallists alone in the second wave) and the 403 London tests, 38.
The IOC said it would conduct four waves of retests in all from 2008 and 2012, with the analysis continuing until after Rio.
"To provide a level playing field for all clean athletes at the Olympic Games Rio 2016, the IOC has already put special measures in place, including targeted pre-tests and the re-analysis of stored samples from the Olympic Games Beijing 2008 and London 2012, following an intelligence-gathering process that started in August 2015," the IOC said on Tuesday.
At the Rio Games which opened on Friday, the IOC is conducting a total of 5500 doping tests, including on the top five finishers and two randomly chosen athletes from every event.
