Green tea extract with a standardized level of catechins in combination with caffeine has been shown to significantly increase daily energy expenditure and fat oxidation over that of caffeine alone . Rudelle and associates  investigated the effects of a thermogenic drink containing green tea catechins, as well as caffeine, on energy expenditure in lean individuals. The beverage increased resting energy expenditure (REE) by 4.6% and the authors suggested that this type of beverage could be beneficial
for weight loss and management. The increase in energy expenditure reported by PS-341 multiple researchers [6–9] positions caffeine and green tea-containing supplements as a beneficial tool to offset the reduction in energy expenditure associated with weight loss [10–12]. In addition to affecting metabolism and favoring fat as a fuel source, many studies have shown that caffeine has an impact on alertness, fatigue, and other mood FG-4592 purchase states [13–15].
After ingesting 120 mg of caffeine supplementation, greater alertness was reported for up to three hours by Mitchell and colleagues  and 40 mg of caffeine combined with 97 mg of L-theanine, the key caffeine analog in tea, showed improvements in perceived alertness and tiredness 20 and 70 minutes after ingestion in an investigation led by Giesbrecht and associates . Caffeine levels of 250 mg and 500 mg also decreased reported tiredness and increased self-reported alertness when given to nine healthy subjects . One important consideration in caffeine consumption studies is the control of habitual intake as individuals can become acclimated to caffeine, thus influencing their physiological responses to a specific dose. Seeing these potential benefits for their consumers, supplement companies have created their
Aldol condensation own proprietary blends for weight management and body leaning supplements, as well as ergogenic aids containing caffeine. Many of these products claim to increase metabolism and “fat burning” either independently, or in conjunction with the caffeine contained in the supplement. Because of the popularity of weight management supplements, researchers have investigated different thermogenic products to determine their effectiveness. For instance, Hoffman and colleagues  determined that a commercially available product containing multiple trademarked ingredient mixtures demonstrated a trend for increased fat oxidation while also increasing heart rate (HR), systolic blood pressure (SBP) and reported levels of tension and confusion among the supplement group. Another study performed in 2009  revealed that capsaicin, an active ingredient in the DBX proprietary blend, statistically increased energy expenditure and diastolic blood pressure (DBP) after ingestion but had no influence on fat utilization.