Rhodiola rosea (RR) is an adaptogenic herb suggested to improve exercise and cognitive performance and reduce stress responses. Further, some evidence reports that L-carnitine (LC) can alter metabolism during exercise and improve performance. This study examined the effects of acute ingestion of a commercially available RR beverage (250 mg, 3% Rosavin) with and without LC (500 mg) on exercise performance, cognitive function and salivary cortisol. In a double-blind, randomised, crossover-design, 18 healthy, active men and women (age, 21±6 years; maximal oxygen uptake, VO2max 43±9 ml/min/kg) consumed 250 ml of a RR-LC, RR and placebo beverage 45 min before a cycle to fatigue at 77±11% of VO2max. Immediately before and after exercise, computerised cognitive tasks of Rapid Visual Information Processing (RVP), Visual Recognition Memory (VRM) and Stroop Colour-Word (Stroop) were completed. Expired gas and heart rate were recorded continuously during exercise. Capillary blood samples were taken for lactate analysis 2 min after cycling and saliva samples were collected before beverage ingestion, before and immediately after cognitive tests for cortisol analysis. Data were analysed using repeated measures ANOVAs with significance set at P<0.05. Time to fatigue, physiological and cognitive variables did not differ between treatments. Cortisol increased (P=0.028) after tests, but there was no effect of treatment on this response. However, exercise elicited higher RVP sustained attention (P<0.05), a faster response time in Stroop (P<0.05), but VRM was reduced. These findings suggest that acute RR-LC ingestion does not alter cognitive function, exercise performance or salivary cortisol. However, chronic supplementation or greater dosage might affect these results. These results show that exhaustive exercise reduces reaction time and increases attention, but memory outcomes become decreased.