A sample that Halep provided during the US Open in August showed traces of Roxadustat, a drug that stimulates the production of red blood cells and is used in the treatment of patients with kidney problems, the International Tennis Integrity Agency (ITIA) said.
Halep, the current world number nine, said the positive test was "the biggest shock of my life".
"Throughout my whole career, the idea of cheating never even crossed my mind once, as it is totally against all the values I have been educated with," the Romanian tweeted. "I will fight until the end to prove that I never knowingly took any prohibited substance and I have faith that sooner or later, the truth will come out."