London 2012 gold medallist Mariya Savinova has been stripped of her 800m title and banned until 2019 after being found guilty of doping.
She has had her results from July 2010 to August 2013 annulled but has 45 days to appeal against the decision.
The Russian beat South Africa's Caster Semenya into second at the London Olympics and the 2011 Worlds in Daegu.
Savinova, 31, also beat Britain's Jenny Meadows into to bronze at the 2010 European Championships.
Both Semenya and Meadows could now have their medals upgraded.
Savinova has also lost her 800m silver from the 2013 Worlds and her four-year suspension will be backdated to 2015.
The case against Savinova was brought by the IAAF based upon her biological passport, which the Court of Arbitration for Sport (Cas) has used to make its decision.
A Cas statement read: "On the basis of clear evidence, including the evidence derived from her biological passport (ABP), Mariya Savinova is found to have been engaged in using doping from 26 July 2010 (the eve of the European Championship in Barcelona) through to 19 August 2013 (the day after the World Championship in Moscow).
"As a consequence, a four-year period of ineligibility, beginning on 24 August 2015, has been imposed and all results achieved between 26 July 2010 and 19 August 2013, are disqualified and any prizes, medals, prize and appearance money forfeited."
Savinova was one of five Russian athletes named in a World Anti-Doping Agency (Wada) report into doping.
She has not raced since 2013 after being suspended during an investigation sparked by the release of undercover footage filmed by whistleblower Yuliya Stepanova.
Should the International Olympic Committee decide to reallocate the medals from the London 2012 final, Semenya would be awarded a second gold after she claimed the 800m title in Rio last summer.
Savinova is now the second Russian finalist from that race to have been retrospectively banned - after Yelena Arzhakova - while a third - bronze medallist Ekaterina Poistogova - is also under investigation for doping.
Richard Conway, BBC Radio 5 live sports news correspondent
Savinova is one of Russia's best known middle-distance athletes - she is now one of Russia's best known drugs cheats.
It means in effect Savinova loses her London 2012 gold medal and Caster Semenya will likely be promoted from silver to gold.
So while there are consequences for Savinova, the world of sporting detection is once again showing it will catch up with athletes if they have cheated even if it is some years after the event.