Caffeine is one of the most commonly consumed pharmacologically active substances in the world. The main sources are coffee, tea, various soft drinks (Coca-Cola, energy drinks), products consisting of cocoa or chocolate, and various medications. A systematic review of the effects of caffeine on human health has found that daily intake of up to 400 mg/day is not associated with negative health effects. However, caffeine consumed at a dose of 3-6 mg/kg body weighwas found to have potentially beneficial ergogenic effects. The ergogenic effect was tested using the 300 m sprint test, a long sprint test used to assess anaerobic running ability. Due to the widespread consumption of caffeine in the population and the large amount of conflicting research, the aim of this study is to examine the relationship between caffeine and 300 m running speed in young adults and to compare the relationship between caffeine and running speed between men and women. The participants of the study were young adults aged 20-40 years from the Primorsko-Goranska County area. According to the results of the Consumption Questionnaire Revised (CCQ-R), they were moderate caffeine consumers and individuals who did not engage in regular physical activity (Category 1 or 2 according to the International Physical Activity Questionnaire (IPAQ-), and they were in good health as assessed by general questionnaire. The measurements were taken in the early morning hours on an athletic track. The first measurement on the participants was performed on all 20 subjects without caffeine supplementation. The second measurement was taken 4 days later. Subsequently, one group of participants (10 subjects) received powdered caffeine, while the other group received a placebo (dextrose). Analysis of the data obtained from measuring the experimental and placebo groups, showed that taking caffeine at a dose of 3 mg/kg body weight had noeffect on running speed and that there was no difference in the impact of caffeine on running speed between men and women. A possible reason for this could be the low dose of caffeine used in this study and the fact that the selected group of participants belonged to the moderate caffeine consumers, wich leads to a lower caffeine effect throuhgt repeated consumption. A well defined and researched methodology is needed to reach more concrete conclusions.