Asian ginseng, the root herb, is traditionally said to improve both mental and physical performance; however, those claims have yet to be proved.  To date, research studies on Asian ginseng have been small or have had design and reporting flaws, and some claims are based on the results of animal research only.  Nevertheless, ginseng is a popular ingredient in energy drinks.  When taken in small doses, ginseng is usually well-tolerated.  Side-effects, when reported, include headaches and sleep and gastrointestinal problems.  Read about ginseng from the Guide to Alternative Medicine at About.com.