The Athletics Integrity Unit said Monday a "notice of allegation" was sent to Adekoya, a Nigerian-born runner who switched allegiance to Bahrain.
The AIU said on its website the 25-year-old Adekoya tested positive for stanozolol - the steroid sprinter Ben Johnson used at the 1988 Seoul Olympics - in November.
Last August at the Asian Games, she took gold in the 400-meter hurdles and 4x400 mixed relay.
Adekoya switched to Bahrain before the 2014 Asian Games and won the 400 and 400 hurdles. In 2016, she was world indoor champion in the 400, and competed in the 400 at the Rio de Janeiro Olympics.
Also Monday, the AIU imposed a two-year ban on Kenyan distance runner Lucy Kabuu for a positive test for morphine.
Kabuu had her results stripped from April to August, including victory at the Milan Marathon, and is banned through July 2020.
She still ranks in the top-30 all-time list in women's marathon for a winning run in Dubai in 2012. A 10,000-meter specialist on the track, Kabuu was the 2006 Commonwealth Games champion and represented Kenya at the 2004 Athens Olympics and 2008 Beijing Olympics, placing fifth.
