BJSM reviews: A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance Part 6

[...]it has been suggested that the benefits of caffeine seen in controlled studies may be overstated, and may actually be explained as the reversal of adverse withdrawal symptoms rather than an ergogenic effect of caffeine per se. 10 It can also increase the risk, with subsequent caffeine intake, of the negative effects often seen with large caffeine doses (irritability, tremor, heart rate increases).