Sceletium tortuosum (Zembrin®) ameliorates experimentally induced anxiety in healthy volunteers

Jonathon Reay, Mark Wetherell

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)
15 Downloads (Pure)


Objective: To investigate the anxiolytic properties of a standardized extract of Sceletium tortuosum (trademarked―Zembrin ®). Methods: Two studies utilized a placebo-controlled, double-blind, between-subject experimental design to investigate the effects of a single dose of Sceletium tortuosum (25 mg, Zembrin ®) on laboratory stress/anxiety responding in 20 young healthy volunteers. To elicit feelings of stress/anxiety, participants completed 20 min of the multitasking framework in study 1 and a 5-min simulated public speaking task in study 2. Study 1 measured subjective experiences of mood at baseline, prestress induction, and poststress induction. Study 2 measured subjective experiences of anxiety and physiological indicators of stress (heart rate [HR] and galvanic skin response) at baseline, prestress induction, during stress induction, and poststress induction. Results: A series of analysis of covariances (baseline entered as the covariate) revealed no treatment effect in study 1; however, study 2 revealed subjective anxiety levels to be significantly lower in the Zembrin ® group at the prestress induction point and a significant interaction between treatment and time on HR. Taken together, results indicate that a single dose of Zembrin ® can ameliorate laboratory stress/anxiety responding in healthy volunteers. Conclusion: We provide the first tentative behavioral evidence to support the anxiolytic properties of Sceletium tortuosum (25 mg Zembrin ®).


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