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

Hum Psychopharmacol. 2020 Nov;35(6):1-7. doi: 10.1002/hup.2753. Epub 2020 Aug 6.


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® ).

Keywords: Sceletium tortuosum; anxiety; anxiolytic; stress; zembrin.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adolescent
  • Aizoaceae / chemistry*
  • Anti-Anxiety Agents / isolation & purification
  • Anti-Anxiety Agents / pharmacology*
  • Anxiety / drug therapy*
  • Double-Blind Method
  • Female
  • Humans
  • Male
  • Plant Extracts / pharmacology*
  • Treatment Outcome
  • Young Adult


  • Anti-Anxiety Agents
  • Plant Extracts