This depends on the user. Caffeine will certainly hurt the athletic performance of individuals who are sensitive to the effects of caffeine. So if you get “caffeine jitters,” don’t use it. Caffeine is also a mild diuretic. If you are not well hydrated to begin with, caffeine may exacerbate your dehydration, which will hurt performance. Caffeine is also a natural cathartic, so if you are getting ready to compete in a long race and are sensitive to this effect of caffeine, it may not be very helpful, either. Caffeine is the most widely used drug in the world. In the athletic world caffeine has been touted as an energy-promoting and fat-burning aid. In athletic competition, caffeine is a “controlled or restricted drug” and is banned by the International Olympic Committee if urine levels exceed allowable limits. It is also banned by the NCAA in amounts that exceed urine levels of 12 micrograms of caffeine per milliliter of urine. Numerous research studies have examined the influence of caffeine on athletic performance. The results are not crystal clear, but laboratory studies have shown that moderate doses of caffeine (3 to 9 milligrams per kilogram of body weight) at least one hour prior to exercise can enhance exercise performance. (A typical 5 to 6 ounce cup of brewed coffee contains approximately 100 milligrams of caffeine.) Note that the research has shown positive impacts on performance primarily when the subjects have been trained athletes who habitually use caffeine. The majority of this research has been done in laboratories rather than at actual competitions, so no one is really sure if it works in the field the same way it does in the laboratory. According to the researchers, many factors can affect exercise performance and the physiological response to caffeine during exercise, including a person’s typical or habitual caffeine intake. Caffeine appears to increase fat oxidation (burning) at rest, but it does not increase fat oxidation after the first few minutes of exercise. The use of caffeine as a significant fat-burning aid during exercise is not supported by the scientific literature.