Former European indoor 800-metre champion Nataliya Lupu of Ukraine will miss this week's world indoor championships in Portland after testing positive for meldonium, the same substance which led to Maria Sharapova's positive test at the Australian Open.

The Ukrainian track and field federation said Lupu withdrew from the championships, which begin Thursday, after the World Anti-Doping Agency "raised concerns about the use of meldonium."

The IAAF later confirmed that "there is a meldonium finding against" Lupu, who won European indoor gold in 2013 and world indoor silver the year before.

In a statement on the federation website, Lupu said she had used meldonium for 15 years for medical reasons with doctors' prescriptions because of "certain changes in my cardiogram."

Lupu said she stopped taking the drug in November, two months before it was officially banned.

"This time was enough for it to leave my body" before the Jan. 1 deadline, she said.

Lupu served a nine-month doping ban after testing positive for the banned stimulant methylhexaneamine at the 2014 world indoors in Sopot, Poland.

Besides Lupu, at least 19 athletes from four countries have been provisionally suspended after testing positive for meldonium, including four Olympic medalists. WADA said in September that meldonium, a popular heart medication in former Soviet nations, would be banned from Jan. 1, citing evidence that it enhanced performance and was being widely used by athletes who did not need it for medical reasons.