[Caffeine, the most frequently consumed psychostimulant: a narrative review article]

Caffeine is the worldwide most frequently consumed psychostimulant. Its availability is nearly unlimited and in Europe it is not subject to state regulation. Apart from its primary role as an ingredient or additive in numerous beverages it also has medical use in apnea of prematurity, as an adjuvant in pain therapy and has regulatory approval for the short-term treatment of symptoms of fatigue. In doses typically administered caffeine's mechanism of action as a psychostimulant is presumably primarily based on central antagonism at adenosine receptors (A₁- und A_2A-receptors), which facilitates central inhibition of adenosine-mediated reduction of the activity of the dopaminergic and ascending arousal system. Metabolisation of caffeine mainly depends on cytochrome P450 1A2. Thus, factors that influence the activity of CYP 1A2 (e. g. medication, pregnancy), may induce remarkable changes of pharmacokinetic parameters. Caffeine improves vigilance, attention and reaction time, particularly in sleep-deprived individuals. Moreover, it may improve endurance performances in sports and muscle strength. Intoxications with caffeine are rare, however can be fatal. In general, caffeine use seems not harmful within typical doses of intake. Caffeine features several, however not all characteristics of potentially addictive drugs; withdrawal after termination of a longer period of use and tolerance are known. In the DSM-5 "caffeine use disorder" is categorized as a possible future disorder that currently needs further study. The pattern of caffeine use of patients should be considered in the medical practice.