Dietary supplementation is commonly employed by individuals seeking to improve body composition and exercise performance. The purpose of the present study was to examine the safety and effectiveness of a commercially available dietary supplement designed to promote thermogenesis and fat loss. In a randomized double-blind trial, participants were assigned to consume placebo or a multi-ingredient supplement containing caffeine, green tea extract, l-carnitine, evodiamine and other ingredients that purportedly enhance thermogenesis. The study included acute baseline testing, a 6-week progressive resistance training and supplementation intervention, and post-intervention testing. Laboratory assessments included resting energy expenditure responses to acute supplement ingestion, evaluation of body composition and muscular performance, and analysis of blood variables (metabolic panel, testosterone, estrogen and cortisol). Dependent variables were analyzed using ANOVA with repeated measures. No unfavorable effects of supplementation were reported, and the supplement did not adversely affect safety markers. However, the supplement did not reduce fat mass or increase lean mass relative to placebo. In the supplement group, lower body maximal strength was increased relative to placebo (+18%, d=1.1 vs. +10%, d=0.5), and cortisol concentrations were decreased relative to placebo (-16%; d=-0.4 vs. +15%, d=.75). However, no differences were observed for upper body maximal strength or muscular endurance. REE increased in response to both supplement and placebo ingestion (placebo: +5%; supplement: +11.5%), but the difference between conditions was not statistically significant. Overall, some select parameters may have been beneficially modified by supplementation, but this did not result in superior weight or fat loss over 6 weeks of supplementation and resistance training.

• A multi-ingredient dietary supplement designed to promote thermogenesis and fat loss appears to be safe to consume for at least 6 weeks in healthy young adults.

• Supplement ingestion acutely increases resting energy expenditure, but this was not significantly greater than increases seen with placebo.

• When combined with a 6-week resistance training program, daily ingestion of the supplement did not produce superior changes in fat mass or lean mass relative to placebo.

• Supplementation for 6 weeks reduced cortisol concentrations relative to placebo, but the physiological impact of this change is likely irrelevant.