Stimulants, together with anabolic androgenic steroids, are regarded as one of the most popular doping substances in sport. Owing to a great variety of these substances and new designer drugs being introduced to the market, each year the World Anti-Doping Agency (WADA) updates the list of substances and methods prohibited in sport. On 1 January 2014, a new doping agent - trimetazidine (TMZ) - was added to the WADA Prohibited List. TMZ, a substance prohibited in competition, is classified in the S6b Specified Stimulant Group. TMZ is used as a well-known cardiologic drug with confirmed biochemical and clinical activity. According to knowledge of the pharmacology and mechanism of TMZ action, TMZ can be used by athletes to improve physical efficiency, especially in the case of endurance sports. This study presents the phenomena of TMZ use by Polish athletes involved in anti-doping control in the WADA-accredited laboratory in Warsaw (Poland) between 2008 and 2013. Samples were taken from the athletes of such disciplines as cycling, athletics, and triathlon. Moreover, the elimination study of TMZ has been conducted to establish the change of TMZ concentration in urine sample after oral administration of a single or double (during the long-term therapy) dose. TMZ was monitored in urine samples by gas chromatography-mass spectrometry-nitrogen phosphorus detection (GC-MS-NPD).