Do you drink coffee? Diet soda? Red Bull? Tea? If so, you are a "user." And caffeine is one of the most widely used drugs in the world. Aside from giving a morning pick-me-up, the use of caffeine to enhance athletic performance has continued to increase in recent years. Such drinks are marketed heavily to an athletic population, promising to enhance performance and increase energy levels.

Common reasoning for caffeine consumption in conjunction with exercise include increasing exercise time to exhaustion, increasing fat oxidation, sparing carbohydrate use during exercise, improving endurance performance, and the thought that caffeine may help delay fatigue.

Caffeine stimulates the nervous system and influences a wide variety of metabolic processes including cardiovascular function and epinephrine release. Due to all of these factors, caffeine may help delay fatigue and enhance performance, but not without possible risks.

Research supports the notion that caffeine can enhance physical performance.

Caffeine appears to have a beneficial effect on alertness and reaction time, when combined with carbohydrate; it also has been shown to improve cognitive function. Caffeine may also decrease the rate of perceived exertion, thereby improving performance so this too could benefit the athlete.

There are mixed findings as to whether or not caffeine has a beneficial effect on high-intensity, short-duration aerobic and anaerobic exercise. However, there is more concrete evidence of a relationship between caffeine intake and improved aerobic endurance activities.

One study tested the effects of different doses of caffeine on cycling performance. They supplemented well-trained cyclists with either 0, 5, 9, or 13 mg/kg of total bodyweight with encapsulated caffeine one hour before they cycled at a high intensity (80% VO2max) until exhaustion. The results showed a significant increase in endurance performance for each of the caffeine doses when compared with placebo, but not with each other.

Most research suggests 1-3 mg caffeine/kg bodyweight (equal to 0.45–1.36 mg/lb) is an effective dose. To have benefit, caffeine is typically ingested 30-60 minutes prior to and/or during exercise.

While a moderate intake of caffeine is considered safe, large doses can be dangerous. No more than 8-10 mg/kg of body weight is recommended, which amounts to approximately 4 to 6 - 8 oz cups of coffee daily.

Caffeine in doses that exceed 10 to 14 grams (or 150 to 200 mg/kg body weight) can be fatal. Individual sensitivity and tolerance to caffeine can vary.

Side effects may include increased anxiety and jitters, sleep disturbances, and GI distress.

Dr Chris Mohr is the creator of Dietary Supplement University ( THE leading resource for the most up to date reviews of ingredients and dietary supplements).