Doping is one of the major problems of modern sport. It is defined as a violation of one or more anti-doping rules defined by the World Anti-Doping Code. Tetrahydrocannabinol is also among doping substances, according to the three WADA criteria. It origins from the plant Cannabis sativa, Cannabinaceae. It is a psychoactive cannabinoid with the strongest activity. Pharmacokinetic and pharmacodynamic mechanisms are responsible for his actions. Depending on the method of application the absorption varies from faster by inhalation to slower by oral ingestion. THC significantly binds to proteins ( 98 % ) and the volume of distribution ( Vd ) is 10 L / kg. THC is metabolized in the liver by hydroxylation, and his half-life is 25 to 57 hours. The hydroxylated forms is the active form . The most part gets secreted in urine as conjugated glucuronic acid. THC binds to cannabinoid receptors ( CB1 and CB2 ). This fact is responsible for the effects on memory, emotion, cognition and movement. It also causes euphoria, relaxation, changes in perception, time distortion and intensifying of normal sensory experiences. Short-term memory and attention, motor skills and reaction time are skills that are affected by THC use. This fact has been confirmed by studies on the impact of THC on sporting ability and performance. They are mostly based on epidemiological studies, studies of performance, driving and flight in the simulator, and closed / open studies of driving on the track. Nevertheless, they are easily transfered to sports, since it is confirmed that the perceptual features are significantly altered, and the user of THC may have difficulty in maintaining concentration and attention which are all important for high performance sport and performance excellence. The main conclusion of most studies is that if the level of THC in blood goes over 5 ng / mL significant negative effects of THC are beginning to prevail. WADA, as the main organization responsible for maintaining the equality of all athletes on the competition (in terms of purity of doping), fair play and the health of athletes, determined the threshold value above which THC must not be found in urine. It used to be the value of 15 ng / ml, but the new decision from year 2013. is 150 ng / ml. This is not only for athletes protection, but also teammates and opponents, becouse an athlete under the influence of THC does not meet the criteria of sober athletes who can rationally judge and duly respond. That is why athletes need to take responsibility to make sure that the substance does not reach their body for which they could be punished, because that punishment is going to leave consequences for them and their career, there are often consequences of their clubs, teammates and the people around them.