The Swedish Athletics Federation (SAF) has revealed Abeba Aregawi's B sample came back positive for the banned substance meldonium.
The 2013 1500 metres world champion was provisionally suspended by the SAF in February after failing an out-of-competition drug test a month earlier.
An SAF statement revealed Aregawi's B sample showed the presence of meldonium, which was added to the World Anti-Doping Agency's list of prohibited substances on January 1.
The 25-year-old, who has won three gold medals and a silver at major championships, blamed pills received from a doctor in her native Ethiopia for the violation.
"I have previously been given pills by a doctor in Ethiopia that I thought were vitamins. It's my own fault I took these pills without checking," Aregawi said in a statement via her agent Valentinj Trouw of Global Sports Management.
"I also had a meeting with the IAAF, which I want to work with fully. I would like to aplogise to the entire sporting movement in general and Swedish Athletics, my managers and coaches and in particular those who supported me over the years.
"They have all been a great help and a great support to me and I understand that I have hurt them and made them disappointed."
SAF general secretary Stefan Olsson added: "This was an expected outcome so I'm not surprised. Doping is totally unacceptable in Swedish Atheltics. We are at the forefront of anti-doping work, but this is clearly not enough.
"It is pleasing that Abeba has chosen to cooperate with the IAAF in this matter. It's great that as much information as possible is shared with the IAAF in our continued efforts against doping.
"It is absolutely necessary for successful anti-doping work and an important step to restore confidence in athletics."
SAF added it is now working on improving its anti-doping measures.