Shot putter Nadzeya Ostapchuk has been suspended from competition after failing a drugs test and being stripped of her Olympic gold medal.
The Belarusian, 31, won with a throw of 21.36m, but officials found metenolone in a urine sample she provided.
New Zealand's Valerie Adams was elevated from second to first.
The Belarusian Athletics Federation have recommended a one-year ban but the International Association of Athletics Federations have yet to accept it.
Women's shot put final - revised result
- Valerie Adams (New Zealand)
- Evgeniia Kolodko (Russia)
- Lijiao Gong (China)
The head of the Belarusian anti-doping agency, Alexander Vanhadlo, said: "Yefimov confessed that he added the banned drug metenolone into Ostapchuk's food because he was worried by her unimpressive results ahead of the Olympics.
"Yefimov said that he did it at the training base in Belarus just days before the start of the Games without Ostapchuk's knowledge."
Ostapchuk won gold at the
2010 European Championships,
but was second to Adams at the 2011 World Championships. She was competing in her third Olympics in London.
London 2012 saw the biggest anti-doping operation
in the history of the Olympics.
Before the start of the Games, those competing were warned that 150 scientists were set to take 6,000 samples between now and the end of the Paralympic Games.
Every competitor who won a medal at the Olympics was tested.
British discus thrower
Brett Morse apologised
to his Twitter followers after accusing Ostapchuk of doping during the event.
After failing to qualify for the Olympics discus final, he tweeted: "I've had a bad day but it could be worse, I could look like Ostapchuk."