The Great Britain women's quadruple scull crew from last August's World Championships at Dorney Lake have been promoted to gold medal winners.
Grainger and her crew were bitterly disappointment at silver
Debbie Flood, Sarah Winckless, Frances Houghton and Kath Grainger had finished runners-up to Russia.
But Russia'S Olga Samulenkova tested positive for testosterone in a drugs test in July.
It means the Russian crew have been disqualified from the race and must hand back their medals.
"We're obviously delighted for our women's quadruple scull who are now world champions again after also winning the title in 2005," said GB Rowing performance director David Tanner.
"However, this is disappointing news for the sport of rowing which has previously recorded so few doping positives."