Abstract
To investigate the anxiolytic properties of a standardized extract of Sceletium tortuosum (trademarked-Zembrin® ). 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. 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. We provide the first tentative behavioral evidence to support the anxiolytic properties of Sceletium tortuosum (25 mg Zembrin® ).
Highlights
Sceletium tortuosum (L.) N.E.Br. (Mesembryanthemaceae) is used by some tribal people of South Africa to reduce feelings of pain and hunger, ameliorate stress, and enhance mental and physical performance
To the authors' knowledge, the anxiolytic effects of Zembrin® are yet to be investigated in a behavioral study; we report for the first time the results of two behavioral studies that directly tested the anxiolytic properties of Zembrin®
Results of the current studies provide the first tentative behavioral evidence to support the anxiolytic properties of Sceletium tortuosum (25 mg Zembrin®) but fail to replicate the previously reported enhancement of cognitive function
Summary
Sceletium tortuosum (L.) N.E.Br. (Mesembryanthemaceae) is used by some tribal people of South Africa to reduce feelings of pain and hunger, ameliorate stress, and enhance mental and physical performance (see review by Gericke & Viljoen, 2008). A standardized extract of Sceletium tortuosum (trademarked as Zembrin®2) has accumulated a small body of evidence to support its safety, cognitive enhancing, anxiolytic properties, and identified potential biological mechanisms of action. With regards to safety, Nell, Siebert, Chellan, and Gericke (2013) demonstrated that both a low (8 mg) and a higher (25 mg) daily dose of Zembrin® ingested for 3 months were well tolerated in healthy participants. With regard to the anxiolytic effect of Zembrin®, two studies have identified potential biological mechanisms of action, the first demonstrated Zembrin® to be a dual serotonin (5‐HT) transporter blocker and selective inhibitor of phosphodiesterase‐4 (Harvey, Young, Viljoen, & Gericke, 2011) and the second demonstrated a single 25 mg dose of Zembrin® could reduce anxiety‐related amygdala reactivity and attenuated amygdala–hypothalamus coupling in healthy young volunteers 2 h postdose (Terburg et al, 2013). Participants were informed that their speech would be recorded and their performance considered by a panel of experts
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