The sympathetic part of the central nervous system plays an important role in adjusting an organism to the state of maximal alertness and total physical mobilization. The mechanism of the sympathetic nervous system is based on complicated neurophysiological processess in which sympathetic neurotransmitter substances (acetylcholine and catecholamines – adrenaline and noradrenaline) are released. Catecholamines act through specific adrenoreceptors (α1,α2 and β) distributed in different tissues of the body. Apart from receptors, adrenergic neurotransmission involves mechanisms for the active re-uptake and re-storage of released amines, as well as enzymatic breakdown by monoamine oxidase (MAO). Adrenaline functions as a neurotransmitter but also is, by activation of adrenal medulla, secreted to the blood as a hormone. The enhanced production of catecholamines causes in the organism a sequence of events leading to psychic concentration, cardiostimulation, energy substrates mobilization and bronchodilation.  Stimulants (sympathomimetics) are the drugs activating central nervous system by adrenaline and noradrenaline action. Direct sympathomimetics mimic the actions of the naturally occuring catecholamines. Indirect sympathomimetics elevate the concentration of noradrenaline at neuroeffector junctions, because they either inhibit re-uptake (cocaine), facilitate release, slow breakdown by monoamine oxidase (MAO), or exert all three effects (amphetamine, methamphetamine).

Stimulants are able to brighten the mood and arousal, eliminate or decrease feeling of fatigue and to enhance physical performance. However, stimulants exhibit a moderate effect on performance and only when high doses of these substances were applied. The most popular stimulants used for doping purposes are: amphetamine, cocaine, ecstasy and methylphenidate (Ritalin). Nicotine and caffeine are also frequently used as stimulants but they are not banned in sports.