Abstract The aim of this study was to assess the effect of a single dose of ADAPT-232 (a standardised fixed combination of Rhodiola rosea L., Schisandra chinensis (Turcz.) Baill., and Eleutherococcus senticosus Maxim) extracts on mental performance, such as attention, speed and accuracy, in tired individuals performing stressful cognitive tasks. The pilot study (phase IIa) clinical trial took the form of a double-blind, placebo-controlled, randomised, with two parallel groups. Forty healthy females aged between 20-68 years, who claimed to have felt stressed over a long period of time due to living under psychologically stressful conditions were selected to participate in the pilot study. In addition, a Stroop Colour-Word test (Stroop CW) was used to exhaust/prepare the volunteers prior to the d2 test used for assessment of cognitive function of patients. The participants were randomised into two groups, one ( n=20) of which received a single tablet of ADAPT-232 (270 mg), while a second ( n=20) received a single tablet of placebo. The effects of the extract were measured prior to treatment and two hours after treatment using the d2 Test of Attention (d2). The results of the d2 test showed a significant difference (p<0.05) in attention, speed, and accuracy (TN-E scores) between the two treatment groups. The subjects in the ADAPT-232 group quickly (two hours after verum was taken) gained improved attention and increased speed and accuracy during stressful cognitive tasks, in comparison to placebo. There was also a tendency of ADAPT-232 to reduce percentage of errors, which means better accuracy, quality of the work, and degree of care in the volunteers under stressful conditions. No serious side effects were reported, although a few minor adverse events, such as sleepiness and cold extremities, were observed in both treatment groups.