I've just read a paper on kava published in the Australian and New Zealand Journal of Psychiatry ("Kava: a comprehensive review of efficacy, safety, and psychopharmacology" by Jerome Sarris , Emma LaPorte , Isaac Schweitzer ). One section was particularly interesting. The authors wanted to determine the effects of kava on cognition and driving ability. Their conclusions are rather interesting:
"To our knowledge only ten clinical trials have explored the acute (n 7) and chronic (n 3) effects of kava on cognition. Table 3 details human RCTs which have assessed the effects of kava extract on cognition. All trials conducted used similar cognitive measures which primarily assessed facets of visual attention, memory retrieval and psychomotor function. Four out of ten studies suggest improved accuracy and performance on visual attention and working memory measures [51,54], while five out of ten studies found that kava had little or no negative effect on cognitive processes [55,59]. The remain- ing study revealed that kava impaired reaction time [60]. Therefore the current evidence suggests that kava has a positive or benign effect on cognition, while impairing motor skills at higher dosages.
Acute RCTs which have suggested that kava significantly enhances cognitive performance, attribute these effect to specific short-term physiological processes. For example, Thompson and colleagues [51] reported that kava improved performance in the Sperling partial report, and recognition tasks, improving the ability of selective attention, visual processing speed and increased the efficiency of memory retrieval via cues [51]. From the results it was postulated that kava decreased decay time of the presented image from iconic memory, and increased the time in which items are transferred to form a more permanent memory trace. Response accuracy was also significantly increased, indicating again that kava may have beneficial effects on working memory and retrieval processes. This study however found that reaction time was reduced by 40% in comparison to placebo, indicating a potentially negative effect on motor-skill based tasks such as driving. In addition it has also been suggested that the novel pharmacological activity of kava that distinguishes it from synthetic anxiolytics (e.g. benzodiaz- epines) is its ability to inhibit re-uptake of noradrenaline [54]. Research has reported that noradrenaline plays a crucial role in cognitive func- tions associated with the frontal lobes, and it has been implicated in a variety of cognitive processes including attention, memory formation storage and consolidation. Therefore noradrenaline may play a crucial role in the short term biochemical changes which affect cognition in short term and acute kava use.
The RCT conducted by Cairney et al. [60] on chronic high dose kava use, attributes significant cognitive impairment (decline in visual atten- tion accuracy and psychomotor function) to specific brain systems associated with motor coordination and visual attention. The dose- dependent psychomotor effects of kava may reflect disruptions of GABAergically modulated functions [60]. The impaired visual atten- tional effects of kava resemble that of alcohol intoxication, indicating modulations to the GABA-benzodiazepine receptor complex through direct action on sodium-dependent ion channels [27].
While the current evidence on kava and cognition suggests that kava extract has a positive or benign effect on cognition (or at least no rep- licable deleterious effects), there are several factors which may under- lie these observations. The variation of kava dosage in all RCTs should be taken into account. It is difficult to compare the psychopharmaco- logical effects of kava across all ten studies, as each trial differs con- siderably in kava preparation, ingestion, quantity and potency of dosages consumed by subjects. Establishing the exact content of kava- lactones consumed by subjects is also difficult as potency of kava can fluctuate according to the extraction procedure used, especially when kava is prepared in the traditional South Pacific manner [60]. Other factors include utilizing specific targeting the specific kavapyrones which may mediate the beneficial effects of kava and cognition. Most RCTs incorporated the use of whole kava extracts (which is appropri- ate), not assessing which individual kavalactones may be responsible for the effects on cognition or motor skills. Isolated kavalactones kavain and dihydrokavain, however, appear not to be the constituents involved with specifically modulating cognition as both isolated constituents were found to not affect learning and memory faculties [56]. Regard- less, kavain and dihydrokavain may be potentially involved in modulat- ing cognition synergistically with other constituents.
To our knowledge only one study has assessed the potential effects of kava on driving ability. Herberg [61] conducted a random- ized, double-blind, placebo-controlled trial which investigated the effects of 300 mg of kava daily over 15 days on driving ability. Participants were subjected to a battery of tests including measures of concentration, vigilance, optical orientation, motor co-ordination and reaction time under stress. Results showed that kava had no effect on measures of driving performance. Further research is needed to replicate these results and establish the acute and chronic cognitive/ driving effects of kava, as it is a crucial component of the plant’s risk to benefit ratio.
In summary, the current evidence overall suggests that kava extract has a positive or benign effect on cognition [51,54], or at least no replicable deleterious effects [55,59]. Despite the evidence indicat- ing that kava can potentially enhance performance on cognitive tasks (e.g. visual processing and working memory), it is noteworthy to men- tion that reaction time and motor skills are significantly reduced [60]. Thus, caution is advised when driving or operating heavy machinery as psychomotor function can be significantly impaired when kava is cons- umed at higher doses. This should be considered when recommending or consuming kava therapeutically. "
"To our knowledge only ten clinical trials have explored the acute (n 7) and chronic (n 3) effects of kava on cognition. Table 3 details human RCTs which have assessed the effects of kava extract on cognition. All trials conducted used similar cognitive measures which primarily assessed facets of visual attention, memory retrieval and psychomotor function. Four out of ten studies suggest improved accuracy and performance on visual attention and working memory measures [51,54], while five out of ten studies found that kava had little or no negative effect on cognitive processes [55,59]. The remain- ing study revealed that kava impaired reaction time [60]. Therefore the current evidence suggests that kava has a positive or benign effect on cognition, while impairing motor skills at higher dosages.
Acute RCTs which have suggested that kava significantly enhances cognitive performance, attribute these effect to specific short-term physiological processes. For example, Thompson and colleagues [51] reported that kava improved performance in the Sperling partial report, and recognition tasks, improving the ability of selective attention, visual processing speed and increased the efficiency of memory retrieval via cues [51]. From the results it was postulated that kava decreased decay time of the presented image from iconic memory, and increased the time in which items are transferred to form a more permanent memory trace. Response accuracy was also significantly increased, indicating again that kava may have beneficial effects on working memory and retrieval processes. This study however found that reaction time was reduced by 40% in comparison to placebo, indicating a potentially negative effect on motor-skill based tasks such as driving. In addition it has also been suggested that the novel pharmacological activity of kava that distinguishes it from synthetic anxiolytics (e.g. benzodiaz- epines) is its ability to inhibit re-uptake of noradrenaline [54]. Research has reported that noradrenaline plays a crucial role in cognitive func- tions associated with the frontal lobes, and it has been implicated in a variety of cognitive processes including attention, memory formation storage and consolidation. Therefore noradrenaline may play a crucial role in the short term biochemical changes which affect cognition in short term and acute kava use.
The RCT conducted by Cairney et al. [60] on chronic high dose kava use, attributes significant cognitive impairment (decline in visual atten- tion accuracy and psychomotor function) to specific brain systems associated with motor coordination and visual attention. The dose- dependent psychomotor effects of kava may reflect disruptions of GABAergically modulated functions [60]. The impaired visual atten- tional effects of kava resemble that of alcohol intoxication, indicating modulations to the GABA-benzodiazepine receptor complex through direct action on sodium-dependent ion channels [27].
While the current evidence on kava and cognition suggests that kava extract has a positive or benign effect on cognition (or at least no rep- licable deleterious effects), there are several factors which may under- lie these observations. The variation of kava dosage in all RCTs should be taken into account. It is difficult to compare the psychopharmaco- logical effects of kava across all ten studies, as each trial differs con- siderably in kava preparation, ingestion, quantity and potency of dosages consumed by subjects. Establishing the exact content of kava- lactones consumed by subjects is also difficult as potency of kava can fluctuate according to the extraction procedure used, especially when kava is prepared in the traditional South Pacific manner [60]. Other factors include utilizing specific targeting the specific kavapyrones which may mediate the beneficial effects of kava and cognition. Most RCTs incorporated the use of whole kava extracts (which is appropri- ate), not assessing which individual kavalactones may be responsible for the effects on cognition or motor skills. Isolated kavalactones kavain and dihydrokavain, however, appear not to be the constituents involved with specifically modulating cognition as both isolated constituents were found to not affect learning and memory faculties [56]. Regard- less, kavain and dihydrokavain may be potentially involved in modulat- ing cognition synergistically with other constituents.
To our knowledge only one study has assessed the potential effects of kava on driving ability. Herberg [61] conducted a random- ized, double-blind, placebo-controlled trial which investigated the effects of 300 mg of kava daily over 15 days on driving ability. Participants were subjected to a battery of tests including measures of concentration, vigilance, optical orientation, motor co-ordination and reaction time under stress. Results showed that kava had no effect on measures of driving performance. Further research is needed to replicate these results and establish the acute and chronic cognitive/ driving effects of kava, as it is a crucial component of the plant’s risk to benefit ratio.
In summary, the current evidence overall suggests that kava extract has a positive or benign effect on cognition [51,54], or at least no replicable deleterious effects [55,59]. Despite the evidence indicat- ing that kava can potentially enhance performance on cognitive tasks (e.g. visual processing and working memory), it is noteworthy to men- tion that reaction time and motor skills are significantly reduced [60]. Thus, caution is advised when driving or operating heavy machinery as psychomotor function can be significantly impaired when kava is cons- umed at higher doses. This should be considered when recommending or consuming kava therapeutically. "
