This study aimed to evaluate how guayusa tea extract and Lion’s Mane mushroom from the Nordic region affect cognitive performance. Researchers used a controlled experiment with a crossover design, meaning participants tried the guayusa extract, Lion’s Mane, and a placebo at different times. They tested cognitive abilities like attention, working memory, and mental arithmetic before and after taking each substance. The results showed that the guayusa extract improved several aspects of cognitive performance, such as reaction time and correct responses in memory and attention tasks. It also positively affected the participants’ self-reported feelings of mental clarity, focus, mood, and productivity. The Lion’s Mane extract, on the other hand, was found to improve the number of correct attempts in a mental arithmetic task and reaction times in a working memory task. Participants also reported feeling happier and more efficient after taking it. Interestingly, even the placebo improved focus and concentration shortly after ingestion. This highlights the potential psychological effect of just believing you’ve taken a cognitive enhancer. The guayusa extract had a unique effect of increasing blood pressure, whereas Lion’s Mane did not. Both substances improved participants’ subjective feelings of happiness and efficiency, but these feelings occurred sooner with Lion’s Mane. In conclusion, both guayusa tea extract and Lion’s Mane were found to have beneficial effects on cognitive performance and mood, but they worked slightly differently and had different onset times for the perceived benefits.