Traditional Chinese and Ayurvedic medicine has documented the use of various plant-derived nootropics (PDN), or substances that enhance cognitive performance, but which ones are supported by scientific studies conducted in humans and for what specific domains of cognition?
This systematic review involved a total of 256 human trials and systematic reviews identified from six independent searches that were performed in parallel for each neurocognitive domain (NCD).
Human cognition can be divided into six domains according to the latest Diagnostic and Statistical Manual of Mental Disorders: perceptual-motor function, language, learning and memory, social cognition, complex attention, and executive function.
The authors reported the following findings from the review.
Ginkgo biloba (aka ginkgo) was the most prominent PDN, seemingly involved in all NCDs, with a defining role in perceptual-motor function improvement (6 studies).
Bacopa monnieri (aka bacopa) was the second most prominent PDN with a defining role in language (3 studies) and learning and memory improvements (10 studies).
Withania somnifera (aka ashwagandha) demonstrated its defining role in improving social cognition (i.e., anxiety and stress; 7 studies).
Caffeine was the prominent PDN for improvements in attention (4 studies) and executive function (4 studies), and all of the previously mentioned PDNs (ginkgo, bacopa, and ashwagandha) also seemed to improve attention.
Flavonoids appeared to play a small role in all NCDs except executive function, whereas ginseng, salvia, tea, and kava demonstrated some improvements in a few NCDs.
Despite its claims as an antidepressant and mood-stabilizing PDN, St. John’s wort demonstrated negative effects on these NCDs.
Despite the wide span of this review, the results should be interpreted with caution because various different extracts/supplements, doses, and durations of PDN intervention were used, as well as different types of participants and outcome measurement methods. Moreover, the underlying mechanisms are often not clearly understood.
Some plants that have demonstrated cognitive benefits, such as rhodiola-rosea, were also not considered.
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