London 2012 Olympic 1500m champion Asli Cakir Alptekin has been stripped of her gold medal for doping.
The Turkish athlete has also been banned for eight years, the Court of Arbitration for Sport confirmed.
An appeal by world governing body the IAAF was upheld after the 29-year-old was cleared in Turkey.
Straight after the race, Britain's Lisa Dobriskey, who finished ninth, told BBC Radio 5 live: "I don't believe I'm competing on a level playing field."
Alptekin's competitive results since July 2010 have been annulled after abnormal values were found in blood samples.
She served a two-year ban after a positive test as a junior in 2004.
Speaking to 5 live after the punishment was announced, Dobriskey, 31, said: "It was unbelievable how good she looked, running the times that she was running and how dominant she was. I just wasn't comfortable racing her.
"Once an athlete has served a drugs ban and they come back running significantly quicker then they were previously it always arouses suspicion.
"Like in any profession, you are a master of your trade as an athlete. You know the sport and you know how good you need to be to be successful and how hard it is to get there.
"When you see something suspicious or out of the ordinary, it is very rare that you can trust it. There was always that element of suspicion and doubt amongst my fellow athletes, competitors and training partners."
The case comes during a series of allegations of doping in athletics made by the Sunday Times and a German broadcaster.
Last week the IAAF said it was suspending 28 athletes as a result of suspicious findings in doping tests.