Caffeine, a substance discovered in plant raw materials over 200 years ago, has been extensively studied. However, many of the mechanisms of its influence on the human body have not yet been elucidated or have given contradictory results in experiments. The aim of this paper was to review and systematize current knowledge on caffeine and its impacts on the human body. A combined physiological and psychological effect of caffeine consumption has been shown to depend mainly on individual genotype and the frequency as well as degree of exposure to the substance. An example of this is the effect of caffeine on sports results, depending on the genotype as well as the effect on the cardiovascular system. People who regularly consume large amounts of coffee or tea do not have increased blood pressure, in contrast to occasional users. Caffeine has many positive properties, which include a slight increase in energy expenditure by increasing basal metabolic rate and promoting less fat gain, by potential reduction of the expression of genes associated with obesity, which can help maintain correct normal body weight and help its normalization.