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Objectives Guarana (Paullinia cupana) from the Sapindaceae family, native to the Amazon basin, is a natural stimulant herb that can be found in popular energy drinks, pharmaceutical shops or local herb shops. With the use of natural health products increasing, guarana has gained a fair amount of popularity in the past years. In this systematic review, we examined the effects of guarana supplementation on cognitive performance. A secondary objective was to compare guarana with caffeine on cognitive performance. Methods Searches were made in PubMed using the terms ‘Guarana’ or ‘Paullinia cupana’. Filters focused on Controlled Clinical trials. Inclusion criteria were met by studies using interventions with guarana, while focusing on guarana’s effects on cognition. Participants needed to be young, healthy adults. Studies not published in English or Greek were excluded. The last date of our search was March 7, 2019. Results A total of 29 studies were identified and screened. After screening, 17 studies were excluded. The remaining 12 studies were found eligible for data extraction. After reading the full text of the 12 studies, 3 studies were excluded. In the end, 9 studies were found eligible for our systematic review (n = 369 participants). In these studies, guarana showed to improve reaction time and accuracy of performance at cognitive tasks. No significant differences were found when comparing guarana with caffeine. Conclusion Guarana seems to improve reaction time and accuracy of performance at tasks, but no significant effects were found when compared with caffeine. High quality randomized controlled clinical trials with a low risk of bias are needed to further study the herb.

Objectives Rhodiola rosea is an adaptogen herb from the Crassulaceae family, which has been vastly used in the Russian and Chinese medicine. The herb is used against depression, anxiety, mental and physical fatigue and to promote overall health. In this systematic review, we examined the effects of R. rosea on depression, anxiety and mood, as these are the most relevant to mental health. Methods Literature searches were made in PubMed using the term ‘Rhodiola rosea’. Inclusion criteria were: Randomized controlled trials using interventions of R. rosea on any type of participants, while focusing on the effects of the intervention on depression, anxiety or mood. Mixed interventions of R. rosea with other herbs were excluded. Studies not published in English or Greek were excluded. Results A total of 39 randomized controlled trials were identified and their abstract was screened. After screening, a total of 17 papers were excluded because they were focusing on irrelevant outcomes. The full text of the remaining 22 papers was read and an additional 17 papers were excluded. These papers were excluded because they were eventually not focusing on our main outcome or they were using R. rosea interventions with other herbs. In the end, a total of 5 papers (n = 327 participants) were found eligible for our systematic review. In these studies, R. rosea seems to improve the symptoms of mild to moderate depression, symptoms of mild anxiety and to enhance mood. The last date of our search was October 13, 2019. Conclusion Rhodiola rosea supplementation may alleviate symptoms of mild to moderate depression and mild anxiety, while it may also enhance mood. The findings of our review are not definite due to the lack of available experimental data. Randomized controlled trials with a low risk of bias are needed to further study the herb.