The Athletics Integrity Unit, which oversees doping cases in track and field, said Friday that Adekoya tested positive for the banned steroid stanozolol. Her ban is backdated from November 2018.
Adekoya competed for Nigeria but switched allegiance to Bahrain ahead of the 2014 Asian Games. Since then, she's won four Asian Games gold medals and an Asian championship title, plus the 2016 world indoor 400 gold in Portland.
The AIU said Adekoya's results since Aug. 24 last year would be struck out, meaning she loses her Asian Games gold medals in the 400 hurdles and the 4x400 mixed relay. The hurdles gold is due to pass to Vietnam's Quach Thi Lan and the relay gold to India.
Bahrain's longstanding policy of fielding African-born runners has come under scrutiny after Olympic marathon silver medalist Eunice Kirwa was banned for four years last month in a doping case. Another distance runner, Violah Jepchumba, was banned last year.
After countries including Bahrain and Qatar spent years recruiting African runners, the IAAF tightened the rules for changes of allegiance in track in 2018, saying it feared some athletes were being bought and sold by third parties. The new measures include a three-year waiting period and a bar on athletes transferring more than once.
Also Friday, the AIU said Indian distance runner Sanjivani Jadhav has been banned for two years for a positive test for probenecid, which can be used to mask the presence of other banned substances. Jadhav loses the bronze medal she won in the 10,000 at April's Asian championships.