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This study aimed to identify and describe the time course of tolerance to the most common caffeine-induced side effects. Eleven participants took part in a crossover, double-blind placebo-controlled experimental design. In one phase, participants ingested 3 mg/kg/day of caffeine for 20 days, while in another phase, they ingested a placebo. Resting heart rate and blood pressure were measured three times per week during each 20-day phase and a quantitative survey was used to categorise the magnitude of side effects. In the pairwise comparison with the placebo, the ingestion of caffeine increased systolic (+ 7.8 ± 10.1%, P