BACKGROUND: To determine the acute effects of ingesting a thermogenic drink (Celsius, Delray Beach, FL) (TD) on changes in metabolism and lipolysis. METHODS: Healthy college-aged male (23.2 +/- 4.0 y, 177.2 +/- 6.1 cm, 81.7 +/- 11.3 kg, 22.8 +/- 7.3 % fat; n = 30) and female (23.4 +/- 3.1 y, 165.6 +/- 8.7 cm, 62.1 +/- 9.9 kg, 28.3 +/- 7.4 % fat; n = 30) participants were matched according to height and weight to consume 336 ml of the TD or a non-caloric, non-caffeinated placebo (PLA). After a 12 h fast, participants reported for pre-consumption measures of height, weight, heart rate, blood pressure, resting energy expenditure (REE), respiratory exchange ratio (RER), glycerol and free-fatty acid (FFA) concentrations. REE and RER were determined at 60, 120, and 180 min post-consumption. Serum glycerol and FFA concentrations were determined at 30, 60, 120 and 180 min post-consumption. RESULTS: When compared to PLA, TD significantly increased REE at 60, 120 and 180 min (p < 0.05). FFA concentrations were significantly greater in TD compared to PLA at 30, 60, 120 and 180 min post-consumption (p < 0.05). No between-group differences were found in RER. CONCLUSION: Acute TD ingestion significantly increased REE, FFA and glycerol appearance. If sustained, these changes may help to promote weight loss and improve body composition; however, these findings are currently unknown as are the general safety and efficacy of prolonged consumption.