In a statement posted to Instagram, the 31-year-old athlete said that the analysis of the sample showed the presence of a substance that is part of the prescription drugs she takes as part of the treatment for attention deficit disorder.
The Brazilian is expected to be temporarily suspended while her case is considered by USADA.
Silva (11-2-1) defeated Holm via second-round submission for the biggest win of her eight-year MMA career at the July 15 tournament in Las Vegas. Shitara have won four fights in a row since returning to bantamweight in 2022 and are currently top contenders for the vacant division title.