On 31 July 2008, Tomashova was suspended by the IAAF, along with six other Russian track and field athletes, for doping offences.

She was charged under IAAF rules 32.2 (b) and 32.2 (e) for a "fraudulent substitution of urine which is both a prohibited method and also a form of tampering with the doping control process".

[1][2] On 20 October 2008, it was announced that Tomashova, along with six other Russian athletes would receive two-year doping bans for manipulating drug samples.

In addition, all results recorded in competitions from June 21, 2012 to January 3, 2015, including the silver medal at the London 2012 Olympics in the women's 1500 metres, were invalidated.

Tomashova is a 2004 Olympic silver medalist in the 1,500 meters, as well as a two-time world champion (2003 and 2005) in this discipline.