At the IAAFWorld Indoor Championships in 2004 she won the 200 m, but was stripped of the title after testing positive for the banned anabolic steroid stanozolol. She denied all knowledge of how it had happened and during the two-year ban that she has received has vowed to work with the World Anti-Doping Agency promoting sports without drugs, joining Kelli White of the United States of America who also fell foul of the same rules after traces of modafinil were found in her urine sample.
In a statement  she said "It’s an accident, I swear I did not take any banned substances, but I do not deny that they were tested in my samples. It was my negligence."
In 2006, Kapachinskaya's mother died, and this affected her running immensely. In the 2008 Olympics, however, she was in the 400 m final and her result was fifth after Yulia Gushchina but achieved a silver in the 4X400 m relay.
In 2009, she again was in the final of 400 m in the world championships and was 6th. The Russian team which included Kapachinskaya achieved a bronze in the relay.