While there is little scientific evidence to bolster the claims made by many energy supplements on the market, some supplement users feel they are useful, as WebMD explains. Energy supplements can be categorized as stimulants, substances that alter metabolism and substances that affect the burning of calories.
The active ingredient in many stimulant energy-boosting supplements is caffeine, which has been shown to boost the metabolism temporarily, improve mental focus and decrease exhaustion, WebMD reports. Sometimes energy supplements use herbal sources of caffeine, including kola nut, yerba mate, guarana and green tea. Other active ingredients in energy supplements include capsaicin, ginseng and bitter orange. Bitter orange, however, is chemically similar to ephedra, which is a banned ingredient due to health risks.