Russia's Liliya Shobukhova has been stripped of her London and Chicago marathon titles after the International Association of Athletics Federations (IAAF) said on Thursday that all her results since 2009 had been annulled and her two-year doping ban extended by 14 months.
The world governing body for athletics issued a statement saying the Court of Arbitration for Sport (CAS) had ratified a settlement agreement under which Shobukhova's original suspension had been prolonged until March 2016.
Her results over the last six years, it added, had also been struck from the record books.
Organizers of the London Marathon, which Shobukhova won in 2010 and where she finished second in 2011, said they will now be taking court action "to recover the prize and appearance money" paid to the Russian athlete.
Shobukhova, who has also been stripped of her 2009, 2010 and 2011 Chicago titles, was originally suspended after irregularities were detected in her biological passport.
Her original two-year ban ran from January 2013, but the IAAF appealed to CAS "in order to seek an extension on the basis of aggravating circumstances."
The 37-year-old Shobukhova featured in a German documentary in December which alleged systematic doping by Russian athletes.
Nick Bitel, chief executive of the London Marathon, said they would now be seeking financial redress.
"We will take action through the English courts to recover the prize and appearance money paid to Shobukhova in 2010 and 2011," he said in a statement.
"We will do everything we can to ensure cheats are caught and do not benefit from cheating and we continue to work closely with the IAAF and other authorities to improve out-of-competition drug testing."