Purpose: Published evidence on common ingredients of "energy drinks" and other dietary supplements widely used by consumers in hopes of enhancing athletic performance is reviewed.
Summary: Preworkout products- unregulated dietary supplements- typically contain "proprietary blends" of multiple ingredients, including caffeine, dimethylamylamine, creatine, arginine, β-alanine, taurine, and phosphates. While some dietary supplement labels instruct consumers to seek the advice of a health care professional before using the products, the labels usually do not disclose all ingredients or their precise amounts, and evidence to support the purported performance-enhancing benefits is generally lacking. There is limited evidence to support the use of some preworkout supplement ingredients. For example, in one small placebo-controlled study (n = 12), the use of the energy drink Red Bull (containing caffeine and taurine) 40 minutes before a simulated cycling time trial appeared to provide a meaningful ergogenic benefit; in another small study (n = 12), the use of a similar caffeine-containing product (Redline) by strength-trained athletes was found to improve reaction time, energy, and mental focus relative to placebo use. However, published evidence on the use of the other ingredients listed above is scant, inconclusive, or conflicting. Adverse effects reported in association with preworkout supplements include gastrointestinal symptoms, cardiac arrhythmia, blood pressure increases, and potential effects on lipids and blood glucose.
Conclusion: Although evidence exists to support the performance-enhancement efficacy of some preworkout ingredients as standalone agents, published data on combination products are scant, inconclusive, or conflicting. The safety of these products may be compromised if users consume larger-than-recommended amounts or use more than one product.